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diff --git a/man3/sysconf.3 b/man3/sysconf.3 new file mode 100644 index 0000000..a4d14d3 --- /dev/null +++ b/man3/sysconf.3 @@ -0,0 +1,391 @@ +'\" t +.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" Modified Sat Jul 24 17:51:42 1993 by Rik Faith (faith@cs.unc.edu) +.\" Modified Tue Aug 17 11:42:20 1999 by Ariel Scolnicov (ariels@compugen.co.il) +.TH sysconf 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +sysconf \- get configuration information at run time +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <unistd.h> +.PP +.BI "long sysconf(int " "name" ); +.fi +.SH DESCRIPTION +POSIX allows an application to test at compile or run time +whether certain options are supported, or what the value is +of certain configurable constants or limits. +.PP +At compile time this is done by including +.I <unistd.h> +and/or +.I <limits.h> +and testing the value of certain macros. +.PP +At run time, one can ask for numerical values using the present function +.BR sysconf (). +One can ask for numerical values that may depend +on the filesystem in which a file resides using +.BR fpathconf (3) +and +.BR pathconf (3). +One can ask for string values using +.BR confstr (3). +.PP +The values obtained from these functions are system configuration constants. +They do not change during the lifetime of a process. +.\" except that sysconf(_SC_OPEN_MAX) may change answer after a call +.\" to setrlimit( ) which changes the RLIMIT_NOFILE soft limit +.PP +For options, typically, there is a constant +.B _POSIX_FOO +that may be defined in +.IR <unistd.h> . +If it is undefined, one should ask at run time. +If it is defined to \-1, then the option is not supported. +If it is defined to 0, then relevant functions and headers exist, +but one has to ask at run time what degree of support is available. +If it is defined to a value other than \-1 or 0, then the option is +supported. +Usually the value (such as 200112L) indicates the year and month +of the POSIX revision describing the option. +glibc uses the value 1 +to indicate support as long as the POSIX revision has not been published yet. +.\" and 999 to indicate support for options no longer present in the latest +.\" standard. (?) +The +.BR sysconf () +argument will be +.BR _SC_FOO . +For a list of options, see +.BR posixoptions (7). +.PP +For variables or limits, typically, there is a constant +.BR _FOO , +maybe defined in +.IR <limits.h> , +or +.BR _POSIX_FOO , +maybe defined in +.IR <unistd.h> . +The constant will not be defined if the limit is unspecified. +If the constant is defined, it gives a guaranteed value, and +a greater value might actually be supported. +If an application wants to take advantage of values which may change +between systems, a call to +.BR sysconf () +can be made. +The +.BR sysconf () +argument will be +.BR _SC_FOO . +.SS POSIX.1 variables +We give the name of the variable, the name of the +.BR sysconf () +argument used to inquire about its value, +and a short description. +.PP +First, the POSIX.1 compatible values. +.\" [for the moment: only the things that are unconditionally present] +.\" .TP +.\" .BR AIO_LISTIO_MAX " - " _SC_AIO_LISTIO_MAX +.\" (if _POSIX_ASYNCHRONOUS_IO) +.\" Maximum number of I/O operations in a single list I/O call. +.\" Must not be less than _POSIX_AIO_LISTIO_MAX. +.\" .TP +.\" .BR AIO_MAX " - " _SC_AIO_MAX +.\" (if _POSIX_ASYNCHRONOUS_IO) +.\" Maximum number of outstanding asynchronous I/O operations. +.\" Must not be less than _POSIX_AIO_MAX. +.\" .TP +.\" .BR AIO_PRIO_DELTA_MAX " - " _SC_AIO_PRIO_DELTA_MAX +.\" (if _POSIX_ASYNCHRONOUS_IO) +.\" The maximum amount by which a process can decrease its +.\" asynchronous I/O priority level from its own scheduling priority. +.\" Must be nonnegative. +.TP +.BR ARG_MAX " - " _SC_ARG_MAX +The maximum length of the arguments to the +.BR exec (3) +family of functions. +Must not be less than +.B _POSIX_ARG_MAX +(4096). +.TP +.BR CHILD_MAX " - " _SC_CHILD_MAX +The maximum number of simultaneous processes per user ID. +Must not be less than +.B _POSIX_CHILD_MAX +(25). +.TP +.BR HOST_NAME_MAX " - " _SC_HOST_NAME_MAX +Maximum length of a hostname, not including the terminating null byte, +as returned by +.BR gethostname (2). +Must not be less than +.B _POSIX_HOST_NAME_MAX +(255). +.TP +.BR LOGIN_NAME_MAX " - " _SC_LOGIN_NAME_MAX +Maximum length of a login name, including the terminating null byte. +Must not be less than +.B _POSIX_LOGIN_NAME_MAX +(9). +.TP +.BR NGROUPS_MAX " - " _SC_NGROUPS_MAX +Maximum number of supplementary group IDs. +.TP +.BR "" "clock ticks - " _SC_CLK_TCK +The number of clock ticks per second. +The corresponding variable is obsolete. +It was of course called +.BR CLK_TCK . +(Note: the macro +.B CLOCKS_PER_SEC +does not give information: it must equal 1000000.) +.TP +.BR OPEN_MAX " - " _SC_OPEN_MAX +The maximum number of files that a process can have open at any time. +Must not be less than +.B _POSIX_OPEN_MAX +(20). +.TP +.BR PAGESIZE " - " _SC_PAGESIZE +Size of a page in bytes. +Must not be less than 1. +.TP +.BR PAGE_SIZE " - " _SC_PAGE_SIZE +A synonym for +.BR PAGESIZE / _SC_PAGESIZE . +(Both +.B PAGESIZE +and +.B PAGE_SIZE +are specified in POSIX.) +.TP +.BR RE_DUP_MAX " - " _SC_RE_DUP_MAX +The number of repeated occurrences of a BRE permitted by +.BR regexec (3) +and +.BR regcomp (3). +Must not be less than +.B _POSIX2_RE_DUP_MAX +(255). +.TP +.BR STREAM_MAX " - " _SC_STREAM_MAX +The maximum number of streams that a process can have open at any +time. +If defined, it has the same value as the standard C macro +.BR FOPEN_MAX . +Must not be less than +.B _POSIX_STREAM_MAX +(8). +.TP +.BR SYMLOOP_MAX " - " _SC_SYMLOOP_MAX +The maximum number of symbolic links seen in a pathname before resolution +returns +.BR ELOOP . +Must not be less than +.B _POSIX_SYMLOOP_MAX +(8). +.TP +.BR TTY_NAME_MAX " - " _SC_TTY_NAME_MAX +The maximum length of terminal device name, +including the terminating null byte. +Must not be less than +.B _POSIX_TTY_NAME_MAX +(9). +.TP +.BR TZNAME_MAX " - " _SC_TZNAME_MAX +The maximum number of bytes in a timezone name. +Must not be less than +.B _POSIX_TZNAME_MAX +(6). +.TP +.BR _POSIX_VERSION " - " _SC_VERSION +indicates the year and month the POSIX.1 standard was approved in the +format +.BR YYYYMML ; +the value +.B 199009L +indicates the Sept. 1990 revision. +.SS POSIX.2 variables +Next, the POSIX.2 values, giving limits for utilities. +.TP +.BR BC_BASE_MAX " - " _SC_BC_BASE_MAX +indicates the maximum +.I obase +value accepted by the +.BR bc (1) +utility. +.TP +.BR BC_DIM_MAX " - " _SC_BC_DIM_MAX +indicates the maximum value of elements permitted in an array by +.BR bc (1). +.TP +.BR BC_SCALE_MAX " - " _SC_BC_SCALE_MAX +indicates the maximum +.I scale +value allowed by +.BR bc (1). +.TP +.BR BC_STRING_MAX " - " _SC_BC_STRING_MAX +indicates the maximum length of a string accepted by +.BR bc (1). +.TP +.BR COLL_WEIGHTS_MAX " - " _SC_COLL_WEIGHTS_MAX +indicates the maximum numbers of weights that can be assigned to an +entry of the +.B LC_COLLATE order +keyword in the locale definition file. +.TP +.BR EXPR_NEST_MAX " - " _SC_EXPR_NEST_MAX +is the maximum number of expressions which can be nested within +parentheses by +.BR expr (1). +.TP +.BR LINE_MAX " - " _SC_LINE_MAX +The maximum length of a utility's input line, either from +standard input or from a file. +This includes space for a trailing +newline. +.TP +.BR RE_DUP_MAX " - " _SC_RE_DUP_MAX +The maximum number of repeated occurrences of a regular expression when +the interval notation +.B \e{m,n\e} +is used. +.TP +.BR POSIX2_VERSION " - " _SC_2_VERSION +indicates the version of the POSIX.2 standard in the format of +YYYYMML. +.TP +.BR POSIX2_C_DEV " - " _SC_2_C_DEV +indicates whether the POSIX.2 C language development facilities are +supported. +.TP +.BR POSIX2_FORT_DEV " - " _SC_2_FORT_DEV +indicates whether the POSIX.2 FORTRAN development utilities are +supported. +.TP +.BR POSIX2_FORT_RUN " - " _SC_2_FORT_RUN +indicates whether the POSIX.2 FORTRAN run-time utilities are supported. +.TP +.BR _POSIX2_LOCALEDEF " - " _SC_2_LOCALEDEF +indicates whether the POSIX.2 creation of locales via +.BR localedef (1) +is supported. +.TP +.BR POSIX2_SW_DEV " - " _SC_2_SW_DEV +indicates whether the POSIX.2 software development utilities option is +supported. +.PP +These values also exist, but may not be standard. +.TP +.BR "" " - " _SC_PHYS_PAGES +The number of pages of physical memory. +Note that it is possible +for the product of this value and the value of +.B _SC_PAGESIZE +to overflow. +.TP +.BR "" " - " _SC_AVPHYS_PAGES +The number of currently available pages of physical memory. +.TP +.BR "" " - " _SC_NPROCESSORS_CONF +The number of processors configured. +See also +.BR get_nprocs_conf (3). +.TP +.BR "" " - " _SC_NPROCESSORS_ONLN +The number of processors currently online (available). +See also +.BR get_nprocs_conf (3). +.SH RETURN VALUE +The return value of +.BR sysconf () +is one of the following: +.IP \[bu] 3 +On error, \-1 is returned and +.I errno +is set to indicate the error +(for example, +.BR EINVAL , +indicating that +.I name +is invalid). +.IP \[bu] +If +.I name +corresponds to a maximum or minimum limit, and that limit is indeterminate, +\-1 is returned and +.I errno +is not changed. +(To distinguish an indeterminate limit from an error, set +.I errno +to zero before the call, and then check whether +.I errno +is nonzero when \-1 is returned.) +.IP \[bu] +If +.I name +corresponds to an option, +a positive value is returned if the option is supported, +and \-1 is returned if the option is not supported. +.IP \[bu] +Otherwise, +the current value of the option or limit is returned. +This value will not be more restrictive than +the corresponding value that was described to the application in +.I <unistd.h> +or +.I <limits.h> +when the application was compiled. +.SH ERRORS +.TP +.B EINVAL +.I name +is invalid. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR sysconf () +T} Thread safety MT-Safe env +.TE +.sp 1 +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001. +.SH BUGS +It is difficult to use +.B ARG_MAX +because it is not specified how much of the argument space for +.BR exec (3) +is consumed by the user's environment variables. +.PP +Some returned values may be huge; they are not suitable for allocating +memory. +.SH SEE ALSO +.BR bc (1), +.BR expr (1), +.BR getconf (1), +.BR locale (1), +.BR confstr (3), +.BR fpathconf (3), +.BR pathconf (3), +.BR posixoptions (7) |