mirror of git://sourceware.org/git/glibc.git
1616 lines
55 KiB
Plaintext
1616 lines
55 KiB
Plaintext
@node System Configuration, Cryptographic Functions, System Management, Top
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@c %MENU% Parameters describing operating system limits
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@chapter System Configuration Parameters
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The functions and macros listed in this chapter give information about
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configuration parameters of the operating system---for example, capacity
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limits, presence of optional POSIX features, and the default path for
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executable files (@pxref{String Parameters}).
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@menu
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* General Limits:: Constants and functions that describe
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various process-related limits that have
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one uniform value for any given machine.
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* System Options:: Optional POSIX features.
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* Version Supported:: Version numbers of POSIX.1 and POSIX.2.
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* Sysconf:: Getting specific configuration values
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of general limits and system options.
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* Minimums:: Minimum values for general limits.
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* Limits for Files:: Size limitations that pertain to individual files.
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These can vary between file systems
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or even from file to file.
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* Options for Files:: Optional features that some files may support.
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* File Minimums:: Minimum values for file limits.
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* Pathconf:: Getting the limit values for a particular file.
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* Utility Limits:: Capacity limits of some POSIX.2 utility programs.
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* Utility Minimums:: Minimum allowable values of those limits.
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* String Parameters:: Getting the default search path.
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@end menu
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@node General Limits
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@section General Capacity Limits
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@cindex POSIX capacity limits
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@cindex limits, POSIX
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@cindex capacity limits, POSIX
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The POSIX.1 and POSIX.2 standards specify a number of parameters that
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describe capacity limitations of the system. These limits can be fixed
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constants for a given operating system, or they can vary from machine to
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machine. For example, some limit values may be configurable by the
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system administrator, either at run time or by rebuilding the kernel,
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and this should not require recompiling application programs.
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@pindex limits.h
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Each of the following limit parameters has a macro that is defined in
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@file{limits.h} only if the system has a fixed, uniform limit for the
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parameter in question. If the system allows different file systems or
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files to have different limits, then the macro is undefined; use
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@code{sysconf} to find out the limit that applies at a particular time
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on a particular machine. @xref{Sysconf}.
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Each of these parameters also has another macro, with a name starting
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with @samp{_POSIX}, which gives the lowest value that the limit is
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allowed to have on @emph{any} POSIX system. @xref{Minimums}.
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@cindex limits, program argument size
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@deftypevr Macro int ARG_MAX
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@standards{POSIX.1, limits.h}
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If defined, the unvarying maximum combined length of the @var{argv} and
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@var{environ} arguments that can be passed to the @code{exec} functions.
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@end deftypevr
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@cindex limits, number of processes
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@deftypevr Macro int CHILD_MAX
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@standards{POSIX.1, limits.h}
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If defined, the unvarying maximum number of processes that can exist
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with the same real user ID at any one time. In BSD and GNU, this is
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controlled by the @code{RLIMIT_NPROC} resource limit; @pxref{Limits on
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Resources}.
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@end deftypevr
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@cindex limits, number of open files
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@deftypevr Macro int OPEN_MAX
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@standards{POSIX.1, limits.h}
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If defined, the unvarying maximum number of files that a single process
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can have open simultaneously. In BSD and GNU, this is controlled
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by the @code{RLIMIT_NOFILE} resource limit; @pxref{Limits on Resources}.
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@end deftypevr
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@deftypevr Macro int STREAM_MAX
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@standards{POSIX.1, limits.h}
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If defined, the unvarying maximum number of streams that a single
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process can have open simultaneously. @xref{Opening Streams}.
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@end deftypevr
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@cindex limits, time zone name length
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@deftypevr Macro int TZNAME_MAX
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@standards{POSIX.1, limits.h}
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If defined, the unvarying maximum length of a time zone name.
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@xref{Time Zone Functions}.
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@end deftypevr
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These limit macros are always defined in @file{limits.h}.
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@cindex limits, number of supplementary group IDs
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@deftypevr Macro int NGROUPS_MAX
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@standards{POSIX.1, limits.h}
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The maximum number of supplementary group IDs that one process can have.
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The value of this macro is actually a lower bound for the maximum. That
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is, you can count on being able to have that many supplementary group
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IDs, but a particular machine might let you have even more. You can use
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@code{sysconf} to see whether a particular machine will let you have
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more (@pxref{Sysconf}).
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@end deftypevr
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@deftypevr Macro ssize_t SSIZE_MAX
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@standards{POSIX.1, limits.h}
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The largest value that can fit in an object of type @code{ssize_t}.
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Effectively, this is the limit on the number of bytes that can be read
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or written in a single operation.
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This macro is defined in all POSIX systems because this limit is never
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configurable.
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@end deftypevr
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@deftypevr Macro int RE_DUP_MAX
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@standards{POSIX.2, limits.h}
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The largest number of repetitions you are guaranteed is allowed in the
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construct @samp{\@{@var{min},@var{max}\@}} in a regular expression.
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The value of this macro is actually a lower bound for the maximum. That
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is, you can count on being able to have that many repetitions, but a
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particular machine might let you have even more. You can use
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@code{sysconf} to see whether a particular machine will let you have
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more (@pxref{Sysconf}). And even the value that @code{sysconf} tells
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you is just a lower bound---larger values might work.
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This macro is defined in all POSIX.2 systems, because POSIX.2 says it
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should always be defined even if there is no specific imposed limit.
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@end deftypevr
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@node System Options
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@section Overall System Options
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@cindex POSIX optional features
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@cindex optional POSIX features
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POSIX defines certain system-specific options that not all POSIX systems
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support. Since these options are provided in the kernel, not in the
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library, simply using @theglibc{} does not guarantee any of these
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features are supported; it depends on the system you are using.
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@pindex unistd.h
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You can test for the availability of a given option using the macros in
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this section, together with the function @code{sysconf}. The macros are
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defined only if you include @file{unistd.h}.
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For the following macros, if the macro is defined in @file{unistd.h},
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then the option is supported. Otherwise, the option may or may not be
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supported; use @code{sysconf} to find out. @xref{Sysconf}.
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@deftypevr Macro int _POSIX_JOB_CONTROL
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@standards{POSIX.1, unistd.h}
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If this symbol is defined, it indicates that the system supports job
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control. Otherwise, the implementation behaves as if all processes
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within a session belong to a single process group. @xref{Job Control}.
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Systems conforming to the 2001 revision of POSIX, or newer, will
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always define this symbol.
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@end deftypevr
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@deftypevr Macro int _POSIX_SAVED_IDS
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@standards{POSIX.1, unistd.h}
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If this symbol is defined, it indicates that the system remembers the
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effective user and group IDs of a process before it executes an
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executable file with the set-user-ID or set-group-ID bits set, and that
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explicitly changing the effective user or group IDs back to these values
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is permitted. If this option is not defined, then if a nonprivileged
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process changes its effective user or group ID to the real user or group
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ID of the process, it can't change it back again. @xref{Enable/Disable
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Setuid}.
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@end deftypevr
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For the following macros, if the macro is defined in @file{unistd.h},
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then its value indicates whether the option is supported. A value of
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@code{-1} means no, and any other value means yes. If the macro is not
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defined, then the option may or may not be supported; use @code{sysconf}
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to find out. @xref{Sysconf}.
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@deftypevr Macro int _POSIX2_C_DEV
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@standards{POSIX.2, unistd.h}
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If this symbol is defined, it indicates that the system has the POSIX.2
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C compiler command, @code{c89}. @Theglibc{} always defines this
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as @code{1}, on the assumption that you would not have installed it if
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you didn't have a C compiler.
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@end deftypevr
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@deftypevr Macro int _POSIX2_FORT_DEV
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@standards{POSIX.2, unistd.h}
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If this symbol is defined, it indicates that the system has the POSIX.2
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Fortran compiler command, @code{fort77}. @Theglibc{} never
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defines this, because we don't know what the system has.
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@end deftypevr
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@deftypevr Macro int _POSIX2_FORT_RUN
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@standards{POSIX.2, unistd.h}
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If this symbol is defined, it indicates that the system has the POSIX.2
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@code{asa} command to interpret Fortran carriage control. @Theglibc{}
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never defines this, because we don't know what the system has.
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@end deftypevr
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@deftypevr Macro int _POSIX2_LOCALEDEF
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@standards{POSIX.2, unistd.h}
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If this symbol is defined, it indicates that the system has the POSIX.2
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@code{localedef} command. @Theglibc{} never defines this, because
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we don't know what the system has.
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@end deftypevr
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@deftypevr Macro int _POSIX2_SW_DEV
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@standards{POSIX.2, unistd.h}
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If this symbol is defined, it indicates that the system has the POSIX.2
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commands @code{ar}, @code{make}, and @code{strip}. @Theglibc{}
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always defines this as @code{1}, on the assumption that you had to have
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@code{ar} and @code{make} to install the library, and it's unlikely that
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@code{strip} would be absent when those are present.
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@end deftypevr
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@node Version Supported
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@section Which Version of POSIX is Supported
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@deftypevr Macro {long int} _POSIX_VERSION
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@standards{POSIX.1, unistd.h}
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This constant represents the version of the POSIX.1 standard to which
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the implementation conforms. For an implementation conforming to the
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1995 POSIX.1 standard, the value is the integer @code{199506L}.
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@code{_POSIX_VERSION} is always defined (in @file{unistd.h}) in any
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POSIX system.
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@strong{Usage Note:} Don't try to test whether the system supports POSIX
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by including @file{unistd.h} and then checking whether
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@code{_POSIX_VERSION} is defined. On a non-POSIX system, this will
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probably fail because there is no @file{unistd.h}. We do not know of
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@emph{any} way you can reliably test at compilation time whether your
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target system supports POSIX or whether @file{unistd.h} exists.
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@end deftypevr
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@deftypevr Macro {long int} _POSIX2_C_VERSION
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@standards{POSIX.2, unistd.h}
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This constant represents the version of the POSIX.2 standard which the
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library and system kernel support. We don't know what value this will
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be for the first version of the POSIX.2 standard, because the value is
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based on the year and month in which the standard is officially adopted.
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The value of this symbol says nothing about the utilities installed on
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the system.
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@strong{Usage Note:} You can use this macro to tell whether a POSIX.1
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system library supports POSIX.2 as well. Any POSIX.1 system contains
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@file{unistd.h}, so include that file and then test @code{defined
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(_POSIX2_C_VERSION)}.
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@end deftypevr
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@node Sysconf
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@section Using @code{sysconf}
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When your system has configurable system limits, you can use the
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@code{sysconf} function to find out the value that applies to any
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particular machine. The function and the associated @var{parameter}
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constants are declared in the header file @file{unistd.h}.
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@menu
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* Sysconf Definition:: Detailed specifications of @code{sysconf}.
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* Constants for Sysconf:: The list of parameters @code{sysconf} can read.
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* Examples of Sysconf:: How to use @code{sysconf} and the parameter
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macros properly together.
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@end menu
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@node Sysconf Definition
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@subsection Definition of @code{sysconf}
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@deftypefun {long int} sysconf (int @var{parameter})
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@standards{POSIX.1, unistd.h}
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@safety{@prelim{}@mtsafe{@mtsenv{}}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
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@c Some parts of the implementation open /proc and /sys files and dirs
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@c to collect system details, using fd and stream I/O depending on the
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@c case. The returned max value may change over time for NPROCS,
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@c NPROCS_CONF, PHYS_PAGES, AVPHYS_PAGES, NGROUPS_MAX, SIGQUEUE_MAX,
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@c depending on variable values read from /proc at each call, and from
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@c rlimit-obtained values CHILD_MAX, OPEN_MAX, ARG_MAX, SIGQUEUE_MAX.
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This function is used to inquire about runtime system parameters. The
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@var{parameter} argument should be one of the @samp{_SC_} symbols listed
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below.
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The normal return value from @code{sysconf} is the value you requested.
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A value of @code{-1} is returned both if the implementation does not
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impose a limit, and in case of an error.
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The following @code{errno} error conditions are defined for this function:
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@table @code
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@item EINVAL
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The value of the @var{parameter} is invalid.
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@end table
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@end deftypefun
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@node Constants for Sysconf
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@subsection Constants for @code{sysconf} Parameters
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Here are the symbolic constants for use as the @var{parameter} argument
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to @code{sysconf}. The values are all integer constants (more
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specifically, enumeration type values).
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@vtable @code
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@item _SC_ARG_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{ARG_MAX}.
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@item _SC_CHILD_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{CHILD_MAX}.
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@item _SC_OPEN_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{OPEN_MAX}.
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@item _SC_STREAM_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{STREAM_MAX}.
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@item _SC_TZNAME_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{TZNAME_MAX}.
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@item _SC_NGROUPS_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{NGROUPS_MAX}.
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@item _SC_JOB_CONTROL
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_JOB_CONTROL}.
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@item _SC_SAVED_IDS
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_SAVED_IDS}.
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@item _SC_VERSION
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_VERSION}.
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@item _SC_CLK_TCK
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@standards{POSIX.1, unistd.h}
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Inquire about the number of clock ticks per second; @pxref{CPU Time}.
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The corresponding parameter @code{CLK_TCK} is obsolete.
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@item _SC_CHARCLASS_NAME_MAX
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@standards{GNU, unistd.h}
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Inquire about the parameter corresponding to maximal length allowed for
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a character class name in an extended locale specification. These
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extensions are not yet standardized and so this option is not standardized
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as well.
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@item _SC_REALTIME_SIGNALS
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@standards{POSIX.1, unistdh.h}
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Inquire about the parameter corresponding to @code{_POSIX_REALTIME_SIGNALS}.
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@item _SC_PRIORITY_SCHEDULING
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_PRIORITY_SCHEDULING}.
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@item _SC_TIMERS
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_TIMERS}.
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@item _SC_ASYNCHRONOUS_IO
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_ASYNCHRONOUS_IO}.
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@item _SC_PRIORITIZED_IO
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_PRIORITIZED_IO}.
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@item _SC_SYNCHRONIZED_IO
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_SYNCHRONIZED_IO}.
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@item _SC_FSYNC
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_FSYNC}.
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@item _SC_MAPPED_FILES
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MAPPED_FILES}.
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@item _SC_MEMLOCK
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK}.
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@item _SC_MEMLOCK_RANGE
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MEMLOCK_RANGE}.
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@item _SC_MEMORY_PROTECTION
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MEMORY_PROTECTION}.
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@item _SC_MESSAGE_PASSING
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MESSAGE_PASSING}.
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@item _SC_SEMAPHORES
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_SEMAPHORES}.
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@item _SC_SHARED_MEMORY_OBJECTS
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to@*
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@code{_POSIX_SHARED_MEMORY_OBJECTS}.
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@item _SC_AIO_LISTIO_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_AIO_LISTIO_MAX}.
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@item _SC_AIO_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_AIO_MAX}.
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@item _SC_AIO_PRIO_DELTA_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the value by which a process can decrease its asynchronous I/O
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priority level from its own scheduling priority. This corresponds to the
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run-time invariant value @code{AIO_PRIO_DELTA_MAX}.
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@item _SC_DELAYTIMER_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_DELAYTIMER_MAX}.
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@item _SC_MQ_OPEN_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MQ_OPEN_MAX}.
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@item _SC_MQ_PRIO_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_MQ_PRIO_MAX}.
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@item _SC_RTSIG_MAX
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@standards{POSIX.1, unistd.h}
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Inquire about the parameter corresponding to @code{_POSIX_RTSIG_MAX}.
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@item _SC_SEM_NSEMS_MAX
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@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_SEM_NSEMS_MAX}.
|
|
|
|
@item _SC_SEM_VALUE_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_SEM_VALUE_MAX}.
|
|
|
|
@item _SC_SIGQUEUE_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_SIGQUEUE_MAX}.
|
|
|
|
@item _SC_TIMER_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_TIMER_MAX}.
|
|
|
|
@item _SC_PII
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII}.
|
|
|
|
@item _SC_PII_XTI
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_XTI}.
|
|
|
|
@item _SC_PII_SOCKET
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_SOCKET}.
|
|
|
|
@item _SC_PII_INTERNET
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET}.
|
|
|
|
@item _SC_PII_OSI
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI}.
|
|
|
|
@item _SC_SELECT
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_SELECT}.
|
|
|
|
@item _SC_UIO_MAXIOV
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_UIO_MAXIOV}.
|
|
|
|
@item _SC_PII_INTERNET_STREAM
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_STREAM}.
|
|
|
|
@item _SC_PII_INTERNET_DGRAM
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_INTERNET_DGRAM}.
|
|
|
|
@item _SC_PII_OSI_COTS
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_COTS}.
|
|
|
|
@item _SC_PII_OSI_CLTS
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_CLTS}.
|
|
|
|
@item _SC_PII_OSI_M
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_PII_OSI_M}.
|
|
|
|
@item _SC_T_IOV_MAX
|
|
@standards{POSIX.1g, unistd.h}
|
|
Inquire about the value associated with the @code{T_IOV_MAX}
|
|
variable.
|
|
|
|
@item _SC_THREADS
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREADS}.
|
|
|
|
@item _SC_THREAD_SAFE_FUNCTIONS
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to@*
|
|
@code{_POSIX_THREAD_SAFE_FUNCTIONS}.
|
|
|
|
@item _SC_GETGR_R_SIZE_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_GETGR_R_SIZE_MAX}.
|
|
|
|
@item _SC_GETPW_R_SIZE_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_GETPW_R_SIZE_MAX}.
|
|
|
|
@item _SC_LOGIN_NAME_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_LOGIN_NAME_MAX}.
|
|
|
|
@item _SC_TTY_NAME_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_TTY_NAME_MAX}.
|
|
|
|
@item _SC_THREAD_DESTRUCTOR_ITERATIONS
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to
|
|
@code{_POSIX_THREAD_DESTRUCTOR_ITERATIONS}.
|
|
|
|
@item _SC_THREAD_KEYS_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREAD_KEYS_MAX}.
|
|
|
|
@item _SC_THREAD_STACK_MIN
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREAD_STACK_MIN}.
|
|
|
|
@item _SC_THREAD_THREADS_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREAD_THREADS_MAX}.
|
|
|
|
@item _SC_THREAD_ATTR_STACKADDR
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to@*a
|
|
@code{_POSIX_THREAD_ATTR_STACKADDR}.
|
|
|
|
@item _SC_THREAD_ATTR_STACKSIZE
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to@*
|
|
@code{_POSIX_THREAD_ATTR_STACKSIZE}.
|
|
|
|
@item _SC_THREAD_PRIORITY_SCHEDULING
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to
|
|
@code{_POSIX_THREAD_PRIORITY_SCHEDULING}.
|
|
|
|
@item _SC_THREAD_PRIO_INHERIT
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_INHERIT}.
|
|
|
|
@item _SC_THREAD_PRIO_PROTECT
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_POSIX_THREAD_PRIO_PROTECT}.
|
|
|
|
@item _SC_THREAD_PROCESS_SHARED
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the parameter corresponding to
|
|
@code{_POSIX_THREAD_PROCESS_SHARED}.
|
|
|
|
@item _SC_2_C_DEV
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about whether the system has the POSIX.2 C compiler command,
|
|
@code{c89}.
|
|
|
|
@item _SC_2_FORT_DEV
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about whether the system has the POSIX.2 Fortran compiler
|
|
command, @code{fort77}.
|
|
|
|
@item _SC_2_FORT_RUN
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about whether the system has the POSIX.2 @code{asa} command to
|
|
interpret Fortran carriage control.
|
|
|
|
@item _SC_2_LOCALEDEF
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about whether the system has the POSIX.2 @code{localedef}
|
|
command.
|
|
|
|
@item _SC_2_SW_DEV
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about whether the system has the POSIX.2 commands @code{ar},
|
|
@code{make}, and @code{strip}.
|
|
|
|
@item _SC_BC_BASE_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum value of @code{obase} in the @code{bc}
|
|
utility.
|
|
|
|
@item _SC_BC_DIM_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum size of an array in the @code{bc}
|
|
utility.
|
|
|
|
@item _SC_BC_SCALE_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum value of @code{scale} in the @code{bc}
|
|
utility.
|
|
|
|
@item _SC_BC_STRING_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum size of a string constant in the
|
|
@code{bc} utility.
|
|
|
|
@item _SC_COLL_WEIGHTS_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum number of weights that can necessarily
|
|
be used in defining the collating sequence for a locale.
|
|
|
|
@item _SC_EXPR_NEST_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum number of expressions nested within
|
|
parentheses when using the @code{expr} utility.
|
|
|
|
@item _SC_LINE_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum size of a text line that the POSIX.2 text
|
|
utilities can handle.
|
|
|
|
@item _SC_EQUIV_CLASS_MAX
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the maximum number of weights that can be assigned to an
|
|
entry of the @code{LC_COLLATE} category @samp{order} keyword in a locale
|
|
definition. @Theglibc{} does not presently support locale
|
|
definitions.
|
|
|
|
@item _SC_VERSION
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the version number of POSIX.1 that the library and kernel
|
|
support.
|
|
|
|
@item _SC_2_VERSION
|
|
@standards{POSIX.2, unistd.h}
|
|
Inquire about the version number of POSIX.2 that the system utilities
|
|
support.
|
|
|
|
@item _SC_PAGESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the virtual memory page size of the machine.
|
|
@code{getpagesize} returns the same value (@pxref{Query Memory Parameters}).
|
|
|
|
@item _SC_NPROCESSORS_CONF
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the number of configured processors.
|
|
|
|
@item _SC_NPROCESSORS_ONLN
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the number of processors online.
|
|
|
|
@item _SC_PHYS_PAGES
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the number of physical pages in the system.
|
|
|
|
@item _SC_AVPHYS_PAGES
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the number of available physical pages in the system.
|
|
|
|
@item _SC_ATEXIT_MAX
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the number of functions which can be registered as termination
|
|
functions for @code{atexit}; @pxref{Cleanups on Exit}.
|
|
|
|
@item _SC_LEVEL1_ICACHE_SIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the size of the Level 1 instruction cache.
|
|
|
|
@item _SC_LEVEL1_ICACHE_ASSOC
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the associativity of the Level 1 instruction cache.
|
|
|
|
@item _SC_LEVEL1_ICACHE_LINESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the line length of the Level 1 instruction cache.
|
|
|
|
On aarch64, the cache line size returned is the minimum instruction cache line
|
|
size observable by userspace. This is typically the same as the L1 icache
|
|
size but on some cores it may not be so. However, it is specified in the
|
|
architecture that operations such as cache line invalidation are consistent
|
|
with the size reported with this variable.
|
|
|
|
@item _SC_LEVEL1_DCACHE_SIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the size of the Level 1 data cache.
|
|
|
|
@item _SC_LEVEL1_DCACHE_ASSOC
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the associativity of the Level 1 data cache.
|
|
|
|
@item _SC_LEVEL1_DCACHE_LINESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the line length of the Level 1 data cache.
|
|
|
|
On aarch64, the cache line size returned is the minimum data cache line size
|
|
observable by userspace. This is typically the same as the L1 dcache size but
|
|
on some cores it may not be so. However, it is specified in the architecture
|
|
that operations such as cache line invalidation are consistent with the size
|
|
reported with this variable.
|
|
|
|
@item _SC_LEVEL2_CACHE_SIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the size of the Level 2 cache.
|
|
|
|
@item _SC_LEVEL2_CACHE_ASSOC
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the associativity of the Level 2 cache.
|
|
|
|
@item _SC_LEVEL2_CACHE_LINESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the line length of the Level 2 cache.
|
|
|
|
@item _SC_LEVEL3_CACHE_SIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the size of the Level 3 cache.
|
|
|
|
@item _SC_LEVEL3_CACHE_ASSOC
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the associativity of the Level 3 cache.
|
|
|
|
@item _SC_LEVEL3_CACHE_LINESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the line length of the Level 3 cache.
|
|
|
|
@item _SC_LEVEL4_CACHE_SIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the size of the Level 4 cache.
|
|
|
|
@item _SC_LEVEL4_CACHE_ASSOC
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the associativity of the Level 4 cache.
|
|
|
|
@item _SC_LEVEL4_CACHE_LINESIZE
|
|
@standards{GNU, unistd.h}
|
|
Inquire about the line length of the Level 4 cache.
|
|
|
|
|
|
@item _SC_XOPEN_VERSION
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_VERSION}.
|
|
|
|
@item _SC_XOPEN_XCU_VERSION
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_XCU_VERSION}.
|
|
|
|
@item _SC_XOPEN_UNIX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_UNIX}.
|
|
|
|
@item _SC_XOPEN_REALTIME
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_REALTIME}.
|
|
|
|
@item _SC_XOPEN_REALTIME_THREADS
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_REALTIME_THREADS}.
|
|
|
|
@item _SC_XOPEN_LEGACY
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_LEGACY}.
|
|
|
|
@item _SC_XOPEN_CRYPT
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_CRYPT}.
|
|
@Theglibc no longer implements the @code{_XOPEN_CRYPT} extensions,
|
|
so @samp{sysconf (_SC_XOPEN_CRYPT)} always returns @code{-1}.
|
|
|
|
@item _SC_XOPEN_ENH_I18N
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_ENH_I18N}.
|
|
|
|
@item _SC_XOPEN_SHM
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_SHM}.
|
|
|
|
@item _SC_XOPEN_XPG2
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_XPG2}.
|
|
|
|
@item _SC_XOPEN_XPG3
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_XPG3}.
|
|
|
|
@item _SC_XOPEN_XPG4
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{_XOPEN_XPG4}.
|
|
|
|
@item _SC_CHAR_BIT
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the number of bits in a variable of type @code{char}.
|
|
|
|
@item _SC_CHAR_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{char}.
|
|
|
|
@item _SC_CHAR_MIN
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the minimum value which can be stored in a variable of type
|
|
@code{char}.
|
|
|
|
@item _SC_INT_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{int}.
|
|
|
|
@item _SC_INT_MIN
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the minimum value which can be stored in a variable of type
|
|
@code{int}.
|
|
|
|
@item _SC_LONG_BIT
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the number of bits in a variable of type @code{long int}.
|
|
|
|
@item _SC_WORD_BIT
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the number of bits in a variable of a register word.
|
|
|
|
@item _SC_MB_LEN_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum length of a multi-byte representation of a wide
|
|
character value.
|
|
|
|
@item _SC_NZERO
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the value used to internally represent the zero priority level for
|
|
the process execution.
|
|
|
|
@item _SC_SSIZE_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{ssize_t}.
|
|
|
|
@item _SC_SCHAR_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{signed char}.
|
|
|
|
@item _SC_SCHAR_MIN
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the minimum value which can be stored in a variable of type
|
|
@code{signed char}.
|
|
|
|
@item _SC_SHRT_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{short int}.
|
|
|
|
@item _SC_SHRT_MIN
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the minimum value which can be stored in a variable of type
|
|
@code{short int}.
|
|
|
|
@item _SC_UCHAR_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{unsigned char}.
|
|
|
|
@item _SC_UINT_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{unsigned int}.
|
|
|
|
@item _SC_ULONG_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{unsigned long int}.
|
|
|
|
@item _SC_USHRT_MAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the maximum value which can be stored in a variable of type
|
|
@code{unsigned short int}.
|
|
|
|
@item _SC_NL_ARGMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_ARGMAX}.
|
|
|
|
@item _SC_NL_LANGMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_LANGMAX}.
|
|
|
|
@item _SC_NL_MSGMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_MSGMAX}.
|
|
|
|
@item _SC_NL_NMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_NMAX}.
|
|
|
|
@item _SC_NL_SETMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_SETMAX}.
|
|
|
|
@item _SC_NL_TEXTMAX
|
|
@standards{X/Open, unistd.h}
|
|
Inquire about the parameter corresponding to @code{NL_TEXTMAX}.
|
|
@end vtable
|
|
|
|
@node Examples of Sysconf
|
|
@subsection Examples of @code{sysconf}
|
|
|
|
We recommend that you first test for a macro definition for the
|
|
parameter you are interested in, and call @code{sysconf} only if the
|
|
macro is not defined. For example, here is how to test whether job
|
|
control is supported:
|
|
|
|
@smallexample
|
|
@group
|
|
int
|
|
have_job_control (void)
|
|
@{
|
|
#ifdef _POSIX_JOB_CONTROL
|
|
return 1;
|
|
#else
|
|
int value = sysconf (_SC_JOB_CONTROL);
|
|
if (value < 0)
|
|
/* @r{If the system is that badly wedged,}
|
|
@r{there's no use trying to go on.} */
|
|
fatal (strerror (errno));
|
|
return value;
|
|
#endif
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
Here is how to get the value of a numeric limit:
|
|
|
|
@smallexample
|
|
int
|
|
get_child_max ()
|
|
@{
|
|
#ifdef CHILD_MAX
|
|
return CHILD_MAX;
|
|
#else
|
|
int value = sysconf (_SC_CHILD_MAX);
|
|
if (value < 0)
|
|
fatal (strerror (errno));
|
|
return value;
|
|
#endif
|
|
@}
|
|
@end smallexample
|
|
|
|
@node Minimums
|
|
@section Minimum Values for General Capacity Limits
|
|
|
|
Here are the names for the POSIX minimum upper bounds for the system
|
|
limit parameters. The significance of these values is that you can
|
|
safely push to these limits without checking whether the particular
|
|
system you are using can go that far.
|
|
|
|
@vtable @code
|
|
@item _POSIX_AIO_LISTIO_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
I/O operations that can be specified in a list I/O call. The value of
|
|
this constant is @code{2}; thus you can add up to two new entries
|
|
of the list of outstanding operations.
|
|
|
|
@item _POSIX_AIO_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
outstanding asynchronous I/O operations. The value of this constant is
|
|
@code{1}. So you cannot expect that you can issue more than one
|
|
operation and immediately continue with the normal work, receiving the
|
|
notifications asynchronously.
|
|
|
|
@item _POSIX_ARG_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum combined length of the @var{argv} and @var{environ}
|
|
arguments that can be passed to the @code{exec} functions.
|
|
Its value is @code{4096}.
|
|
|
|
@item _POSIX_CHILD_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum number of simultaneous processes per real user ID. Its
|
|
value is @code{6}.
|
|
|
|
@item _POSIX_NGROUPS_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum number of supplementary group IDs per process. Its
|
|
value is @code{0}.
|
|
|
|
@item _POSIX_OPEN_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum number of files that a single process can have open
|
|
simultaneously. Its value is @code{16}.
|
|
|
|
@item _POSIX_SSIZE_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum value that can be stored in an object of type
|
|
@code{ssize_t}. Its value is @code{32767}.
|
|
|
|
@item _POSIX_STREAM_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum number of streams that a single process can have open
|
|
simultaneously. Its value is @code{8}.
|
|
|
|
@item _POSIX_TZNAME_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the maximum length of a time zone name. Its value is @code{3}.
|
|
|
|
@item _POSIX2_RE_DUP_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The value of this macro is the most restrictive limit permitted by POSIX
|
|
for the numbers used in the @samp{\@{@var{min},@var{max}\@}} construct
|
|
in a regular expression. Its value is @code{255}.
|
|
@end vtable
|
|
|
|
@node Limits for Files
|
|
@section Limits on File System Capacity
|
|
|
|
The POSIX.1 standard specifies a number of parameters that describe the
|
|
limitations of the file system. It's possible for the system to have a
|
|
fixed, uniform limit for a parameter, but this isn't the usual case. On
|
|
most systems, it's possible for different file systems (and, for some
|
|
parameters, even different files) to have different maximum limits. For
|
|
example, this is very likely if you use NFS to mount some of the file
|
|
systems from other machines.
|
|
|
|
@pindex limits.h
|
|
Each of the following macros is defined in @file{limits.h} only if the
|
|
system has a fixed, uniform limit for the parameter in question. If the
|
|
system allows different file systems or files to have different limits,
|
|
then the macro is undefined; use @code{pathconf} or @code{fpathconf} to
|
|
find out the limit that applies to a particular file. @xref{Pathconf}.
|
|
|
|
Each parameter also has another macro, with a name starting with
|
|
@samp{_POSIX}, which gives the lowest value that the limit is allowed to
|
|
have on @emph{any} POSIX system. @xref{File Minimums}.
|
|
|
|
@cindex limits, link count of files
|
|
@deftypevr Macro int LINK_MAX
|
|
@standards{POSIX.1, limits.h (optional)}
|
|
The uniform system limit (if any) for the number of names for a given
|
|
file. @xref{Hard Links}.
|
|
@end deftypevr
|
|
|
|
@cindex limits, terminal input queue
|
|
@deftypevr Macro int MAX_CANON
|
|
@standards{POSIX.1, limits.h}
|
|
The uniform system limit (if any) for the amount of text in a line of
|
|
input when input editing is enabled. @xref{Canonical or Not}.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int MAX_INPUT
|
|
@standards{POSIX.1, limits.h}
|
|
The uniform system limit (if any) for the total number of characters
|
|
typed ahead as input. @xref{I/O Queues}.
|
|
@end deftypevr
|
|
|
|
@cindex limits, file name length
|
|
@deftypevr Macro int NAME_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The uniform system limit (if any) for the length of a file name component, not
|
|
including the terminating null character.
|
|
|
|
@strong{Portability Note:} On some systems, @theglibc{} defines
|
|
@code{NAME_MAX}, but does not actually enforce this limit.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int PATH_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The uniform system limit (if any) for the length of an entire file name (that
|
|
is, the argument given to system calls such as @code{open}), including the
|
|
terminating null character.
|
|
|
|
@strong{Portability Note:} @Theglibc{} does not enforce this limit
|
|
even if @code{PATH_MAX} is defined.
|
|
@end deftypevr
|
|
|
|
@cindex limits, pipe buffer size
|
|
@deftypevr Macro int PIPE_BUF
|
|
@standards{POSIX.1, limits.h}
|
|
The uniform system limit (if any) for the number of bytes that can be
|
|
written atomically to a pipe. If multiple processes are writing to the
|
|
same pipe simultaneously, output from different processes might be
|
|
interleaved in chunks of this size. @xref{Pipes and FIFOs}.
|
|
@end deftypevr
|
|
|
|
These are alternative macro names for some of the same information.
|
|
|
|
@deftypevr Macro int MAXNAMLEN
|
|
@standards{BSD, dirent.h}
|
|
This is the BSD name for @code{NAME_MAX}. It is defined in
|
|
@file{dirent.h}.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int FILENAME_MAX
|
|
@standards{ISO, stdio.h}
|
|
The value of this macro is an integer constant expression that
|
|
represents the maximum length of a file name string. It is defined in
|
|
@file{stdio.h}.
|
|
|
|
Unlike @code{PATH_MAX}, this macro is defined even if there is no actual
|
|
limit imposed. In such a case, its value is typically a very large
|
|
number. @strong{This is always the case on @gnuhurdsystems{}.}
|
|
|
|
@strong{Usage Note:} Don't use @code{FILENAME_MAX} as the size of an
|
|
array in which to store a file name! You can't possibly make an array
|
|
that big! Use dynamic allocation (@pxref{Memory Allocation}) instead.
|
|
@end deftypevr
|
|
|
|
@node Options for Files
|
|
@section Optional Features in File Support
|
|
|
|
POSIX defines certain system-specific options in the system calls for
|
|
operating on files. Some systems support these options and others do
|
|
not. Since these options are provided in the kernel, not in the
|
|
library, simply using @theglibc{} does not guarantee that any of these
|
|
features is supported; it depends on the system you are using. They can
|
|
also vary between file systems on a single machine.
|
|
|
|
@pindex unistd.h
|
|
This section describes the macros you can test to determine whether a
|
|
particular option is supported on your machine. If a given macro is
|
|
defined in @file{unistd.h}, then its value says whether the
|
|
corresponding feature is supported. (A value of @code{-1} indicates no;
|
|
any other value indicates yes.) If the macro is undefined, it means
|
|
particular files may or may not support the feature.
|
|
|
|
Since all the machines that support @theglibc{} also support NFS,
|
|
one can never make a general statement about whether all file systems
|
|
support the @code{_POSIX_CHOWN_RESTRICTED} and @code{_POSIX_NO_TRUNC}
|
|
features. So these names are never defined as macros in @theglibc{}.
|
|
|
|
@deftypevr Macro int _POSIX_CHOWN_RESTRICTED
|
|
@standards{POSIX.1, unistd.h}
|
|
If this option is in effect, the @code{chown} function is restricted so
|
|
that the only changes permitted to nonprivileged processes is to change
|
|
the group owner of a file to either be the effective group ID of the
|
|
process, or one of its supplementary group IDs. @xref{File Owner}.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int _POSIX_NO_TRUNC
|
|
@standards{POSIX.1, unistd.h}
|
|
If this option is in effect, file name components longer than
|
|
@code{NAME_MAX} generate an @code{ENAMETOOLONG} error. Otherwise, file
|
|
name components that are too long are silently truncated.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro {unsigned char} _POSIX_VDISABLE
|
|
@standards{POSIX.1, unistd.h}
|
|
This option is only meaningful for files that are terminal devices.
|
|
If it is enabled, then handling for special control characters can
|
|
be disabled individually. @xref{Special Characters}.
|
|
@end deftypevr
|
|
|
|
@pindex unistd.h
|
|
If one of these macros is undefined, that means that the option might be
|
|
in effect for some files and not for others. To inquire about a
|
|
particular file, call @code{pathconf} or @code{fpathconf}.
|
|
@xref{Pathconf}.
|
|
|
|
@node File Minimums
|
|
@section Minimum Values for File System Limits
|
|
|
|
Here are the names for the POSIX minimum upper bounds for some of the
|
|
above parameters. The significance of these values is that you can
|
|
safely push to these limits without checking whether the particular
|
|
system you are using can go that far. In most cases @gnusystems{} do not
|
|
have these strict limitations. The actual limit should be requested if
|
|
necessary.
|
|
|
|
@vtable @code
|
|
@item _POSIX_LINK_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum value of a
|
|
file's link count. The value of this constant is @code{8}; thus, you
|
|
can always make up to eight names for a file without running into a
|
|
system limit.
|
|
|
|
@item _POSIX_MAX_CANON
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
bytes in a canonical input line from a terminal device. The value of
|
|
this constant is @code{255}.
|
|
|
|
@item _POSIX_MAX_INPUT
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
bytes in a terminal device input queue (or typeahead buffer).
|
|
@xref{Input Modes}. The value of this constant is @code{255}.
|
|
|
|
@item _POSIX_NAME_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
bytes in a file name component. The value of this constant is
|
|
@code{14}.
|
|
|
|
@item _POSIX_PATH_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
bytes in a file name. The value of this constant is @code{256}.
|
|
|
|
@item _POSIX_PIPE_BUF
|
|
@standards{POSIX.1, limits.h}
|
|
The most restrictive limit permitted by POSIX for the maximum number of
|
|
bytes that can be written atomically to a pipe. The value of this
|
|
constant is @code{512}.
|
|
|
|
@item SYMLINK_MAX
|
|
@standards{POSIX.1, limits.h}
|
|
Maximum number of bytes in a symbolic link.
|
|
|
|
@item POSIX_REC_INCR_XFER_SIZE
|
|
@standards{POSIX.1, limits.h}
|
|
Recommended increment for file transfer sizes between the
|
|
@code{POSIX_REC_MIN_XFER_SIZE} and @code{POSIX_REC_MAX_XFER_SIZE}
|
|
values.
|
|
|
|
@item POSIX_REC_MAX_XFER_SIZE
|
|
@standards{POSIX.1, limits.h}
|
|
Maximum recommended file transfer size.
|
|
|
|
@item POSIX_REC_MIN_XFER_SIZE
|
|
@standards{POSIX.1, limits.h}
|
|
Minimum recommended file transfer size.
|
|
|
|
@item POSIX_REC_XFER_ALIGN
|
|
@standards{POSIX.1, limits.h}
|
|
Recommended file transfer buffer alignment.
|
|
@end vtable
|
|
|
|
@node Pathconf
|
|
@section Using @code{pathconf}
|
|
|
|
When your machine allows different files to have different values for a
|
|
file system parameter, you can use the functions in this section to find
|
|
out the value that applies to any particular file.
|
|
|
|
These functions and the associated constants for the @var{parameter}
|
|
argument are declared in the header file @file{unistd.h}.
|
|
|
|
@deftypefun {long int} pathconf (const char *@var{filename}, int @var{parameter})
|
|
@standards{POSIX.1, unistd.h}
|
|
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
|
|
@c When __statfs_link_max finds an ext* filesystem, it may read
|
|
@c /proc/mounts or similar as a mntent stream.
|
|
@c __statfs_chown_restricted may read from
|
|
@c /proc/sys/fs/xfs/restrict_chown as a file descriptor.
|
|
This function is used to inquire about the limits that apply to
|
|
the file named @var{filename}.
|
|
|
|
The @var{parameter} argument should be one of the @samp{_PC_} constants
|
|
listed below.
|
|
|
|
The normal return value from @code{pathconf} is the value you requested.
|
|
A value of @code{-1} is returned both if the implementation does not
|
|
impose a limit, and in case of an error. In the former case,
|
|
@code{errno} is not set, while in the latter case, @code{errno} is set
|
|
to indicate the cause of the problem. So the only way to use this
|
|
function robustly is to store @code{0} into @code{errno} just before
|
|
calling it.
|
|
|
|
Besides the usual file name errors (@pxref{File Name Errors}),
|
|
the following error condition is defined for this function:
|
|
|
|
@table @code
|
|
@item EINVAL
|
|
The value of @var{parameter} is invalid, or the implementation doesn't
|
|
support the @var{parameter} for the specific file.
|
|
@end table
|
|
@end deftypefun
|
|
|
|
@deftypefun {long int} fpathconf (int @var{filedes}, int @var{parameter})
|
|
@standards{POSIX.1, unistd.h}
|
|
@safety{@prelim{}@mtsafe{}@asunsafe{@asulock{} @ascuheap{}}@acunsafe{@aculock{} @acsfd{} @acsmem{}}}
|
|
@c Same caveats as pathconf.
|
|
This is just like @code{pathconf} except that an open file descriptor
|
|
is used to specify the file for which information is requested, instead
|
|
of a file name.
|
|
|
|
The following @code{errno} error conditions are defined for this function:
|
|
|
|
@table @code
|
|
@item EBADF
|
|
The @var{filedes} argument is not a valid file descriptor.
|
|
|
|
@item EINVAL
|
|
The value of @var{parameter} is invalid, or the implementation doesn't
|
|
support the @var{parameter} for the specific file.
|
|
@end table
|
|
@end deftypefun
|
|
|
|
Here are the symbolic constants that you can use as the @var{parameter}
|
|
argument to @code{pathconf} and @code{fpathconf}. The values are all
|
|
integer constants.
|
|
|
|
@vtable @code
|
|
@item _PC_LINK_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{LINK_MAX}.
|
|
|
|
@item _PC_MAX_CANON
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{MAX_CANON}.
|
|
|
|
@item _PC_MAX_INPUT
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{MAX_INPUT}.
|
|
|
|
@item _PC_NAME_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{NAME_MAX}.
|
|
|
|
@item _PC_PATH_MAX
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{PATH_MAX}.
|
|
|
|
@item _PC_PIPE_BUF
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{PIPE_BUF}.
|
|
|
|
@item _PC_CHOWN_RESTRICTED
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_CHOWN_RESTRICTED}.
|
|
|
|
@item _PC_NO_TRUNC
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_NO_TRUNC}.
|
|
|
|
@item _PC_VDISABLE
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_VDISABLE}.
|
|
|
|
@item _PC_SYNC_IO
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_SYNC_IO}.
|
|
|
|
@item _PC_ASYNC_IO
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_ASYNC_IO}.
|
|
|
|
@item _PC_PRIO_IO
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{_POSIX_PRIO_IO}.
|
|
|
|
@item _PC_FILESIZEBITS
|
|
@standards{LFS, unistd.h}
|
|
Inquire about the availability of large files on the filesystem.
|
|
|
|
@item _PC_REC_INCR_XFER_SIZE
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{POSIX_REC_INCR_XFER_SIZE}.
|
|
|
|
@item _PC_REC_MAX_XFER_SIZE
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{POSIX_REC_MAX_XFER_SIZE}.
|
|
|
|
@item _PC_REC_MIN_XFER_SIZE
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{POSIX_REC_MIN_XFER_SIZE}.
|
|
|
|
@item _PC_REC_XFER_ALIGN
|
|
@standards{POSIX.1, unistd.h}
|
|
Inquire about the value of @code{POSIX_REC_XFER_ALIGN}.
|
|
@end vtable
|
|
|
|
@strong{Portability Note:} On some systems, @theglibc{} does not
|
|
enforce @code{_PC_NAME_MAX} or @code{_PC_PATH_MAX} limits.
|
|
|
|
@node Utility Limits
|
|
@section Utility Program Capacity Limits
|
|
|
|
The POSIX.2 standard specifies certain system limits that you can access
|
|
through @code{sysconf} that apply to utility behavior rather than the
|
|
behavior of the library or the operating system.
|
|
|
|
@Theglibc{} defines macros for these limits, and @code{sysconf}
|
|
returns values for them if you ask; but these values convey no
|
|
meaningful information. They are simply the smallest values that
|
|
POSIX.2 permits.
|
|
|
|
@deftypevr Macro int BC_BASE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest value of @code{obase} that the @code{bc} utility is
|
|
guaranteed to support.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int BC_DIM_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest number of elements in one array that the @code{bc} utility
|
|
is guaranteed to support.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int BC_SCALE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest value of @code{scale} that the @code{bc} utility is
|
|
guaranteed to support.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int BC_STRING_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest number of characters in one string constant that the
|
|
@code{bc} utility is guaranteed to support.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int COLL_WEIGHTS_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest number of weights that can necessarily be used in defining
|
|
the collating sequence for a locale.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int EXPR_NEST_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The maximum number of expressions that can be nested within parentheses
|
|
by the @code{expr} utility.
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int LINE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The largest text line that the text-oriented POSIX.2 utilities can
|
|
support. (If you are using the GNU versions of these utilities, then
|
|
there is no actual limit except that imposed by the available virtual
|
|
memory, but there is no way that the library can tell you this.)
|
|
@end deftypevr
|
|
|
|
@deftypevr Macro int EQUIV_CLASS_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The maximum number of weights that can be assigned to an entry of the
|
|
@code{LC_COLLATE} category @samp{order} keyword in a locale definition.
|
|
@Theglibc{} does not presently support locale definitions.
|
|
@end deftypevr
|
|
|
|
@node Utility Minimums
|
|
@section Minimum Values for Utility Limits
|
|
|
|
@vtable @code
|
|
@item _POSIX2_BC_BASE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum value of
|
|
@code{obase} in the @code{bc} utility. Its value is @code{99}.
|
|
|
|
@item _POSIX2_BC_DIM_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum size of
|
|
an array in the @code{bc} utility. Its value is @code{2048}.
|
|
|
|
@item _POSIX2_BC_SCALE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum value of
|
|
@code{scale} in the @code{bc} utility. Its value is @code{99}.
|
|
|
|
@item _POSIX2_BC_STRING_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum size of
|
|
a string constant in the @code{bc} utility. Its value is @code{1000}.
|
|
|
|
@item _POSIX2_COLL_WEIGHTS_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum number
|
|
of weights that can necessarily be used in defining the collating
|
|
sequence for a locale. Its value is @code{2}.
|
|
|
|
@item _POSIX2_EXPR_NEST_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum number
|
|
of expressions nested within parenthesis when using the @code{expr} utility.
|
|
Its value is @code{32}.
|
|
|
|
@item _POSIX2_LINE_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum size of
|
|
a text line that the text utilities can handle. Its value is
|
|
@code{2048}.
|
|
|
|
@item _POSIX2_EQUIV_CLASS_MAX
|
|
@standards{POSIX.2, limits.h}
|
|
The most restrictive limit permitted by POSIX.2 for the maximum number
|
|
of weights that can be assigned to an entry of the @code{LC_COLLATE}
|
|
category @samp{order} keyword in a locale definition. Its value is
|
|
@code{2}. @Theglibc{} does not presently support locale
|
|
definitions.
|
|
@end vtable
|
|
|
|
@node String Parameters
|
|
@section String-Valued Parameters
|
|
|
|
POSIX.2 defines a way to get string-valued parameters from the operating
|
|
system with the function @code{confstr}:
|
|
|
|
@deftypefun size_t confstr (int @var{parameter}, char *@var{buf}, size_t @var{len})
|
|
@standards{POSIX.2, unistd.h}
|
|
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
|
|
This function reads the value of a string-valued system parameter,
|
|
storing the string into @var{len} bytes of memory space starting at
|
|
@var{buf}. The @var{parameter} argument should be one of the
|
|
@samp{_CS_} symbols listed below.
|
|
|
|
The normal return value from @code{confstr} is the length of the string
|
|
value that you asked for. If you supply a null pointer for @var{buf},
|
|
then @code{confstr} does not try to store the string; it just returns
|
|
its length. A value of @code{0} indicates an error.
|
|
|
|
If the string you asked for is too long for the buffer (that is, longer
|
|
than @code{@var{len} - 1}), then @code{confstr} stores just that much
|
|
(leaving room for the terminating null character). You can tell that
|
|
this has happened because @code{confstr} returns a value greater than or
|
|
equal to @var{len}.
|
|
|
|
The following @code{errno} error conditions are defined for this function:
|
|
|
|
@table @code
|
|
@item EINVAL
|
|
The value of the @var{parameter} is invalid.
|
|
@end table
|
|
@end deftypefun
|
|
|
|
Currently there is just one parameter you can read with @code{confstr}:
|
|
|
|
@vtable @code
|
|
@item _CS_PATH
|
|
@standards{POSIX.2, unistd.h}
|
|
This parameter's value is the recommended default path for searching for
|
|
executable files. This is the path that a user has by default just
|
|
after logging in.
|
|
|
|
@item _CS_LFS_CFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the C compiler if a source is compiled using the
|
|
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS_LDFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the linker if a source is compiled using the
|
|
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS_LIBS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional libraries must be linked
|
|
to the application if a source is compiled using the
|
|
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS_LINTFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the lint tool if a source is compiled using the
|
|
@code{_LARGEFILE_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS64_CFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the C compiler if a source is compiled using the
|
|
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS64_LDFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the linker if a source is compiled using the
|
|
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS64_LIBS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional libraries must be linked
|
|
to the application if a source is compiled using the
|
|
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
|
|
@item _CS_LFS64_LINTFLAGS
|
|
@standards{Unix98, unistd.h}
|
|
The returned string specifies which additional flags must be given to
|
|
the lint tool if a source is compiled using the
|
|
@code{_LARGEFILE64_SOURCE} feature select macro; @pxref{Feature Test Macros}.
|
|
@end vtable
|
|
|
|
The way to use @code{confstr} without any arbitrary limit on string size
|
|
is to call it twice: first call it to get the length, allocate the
|
|
buffer accordingly, and then call @code{confstr} again to fill the
|
|
buffer, like this:
|
|
|
|
@smallexample
|
|
@group
|
|
char *
|
|
get_default_path (void)
|
|
@{
|
|
size_t len = confstr (_CS_PATH, NULL, 0);
|
|
char *buffer = (char *) xmalloc (len);
|
|
|
|
if (confstr (_CS_PATH, buf, len + 1) == 0)
|
|
@{
|
|
free (buffer);
|
|
return NULL;
|
|
@}
|
|
|
|
return buffer;
|
|
@}
|
|
@end group
|
|
@end smallexample
|