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diff --git a/man2/shmget.2 b/man2/shmget.2 deleted file mode 100644 index 685963a..0000000 --- a/man2/shmget.2 +++ /dev/null @@ -1,412 +0,0 @@ -.\" Copyright (c) 1993 Luigi P. Bai (lpb@softint.com) July 28, 1993 -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" Modified Wed Jul 28 10:57:35 1993, Rik Faith <faith@cs.unc.edu> -.\" Modified Sun Nov 28 16:43:30 1993, Rik Faith <faith@cs.unc.edu> -.\" with material from Giorgio Ciucci <giorgio@crcc.it> -.\" Portions Copyright 1993 Giorgio Ciucci <giorgio@crcc.it> -.\" Modified Tue Oct 22 22:03:17 1996 by Eric S. Raymond <esr@thyrsus.com> -.\" Modified, 8 Jan 2003, Michael Kerrisk, <mtk.manpages@gmail.com> -.\" Removed EIDRM from errors - that can't happen... -.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Added notes on capability requirements -.\" Modified, 11 Nov 2004, Michael Kerrisk <mtk.manpages@gmail.com> -.\" Language and formatting clean-ups -.\" Added notes on /proc files -.\" -.TH shmget 2 2023-10-31 "Linux man-pages 6.7" -.SH NAME -shmget \- allocates a System V shared memory segment -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <sys/shm.h> -.P -.BI "int shmget(key_t " key ", size_t " size ", int " shmflg ); -.fi -.SH DESCRIPTION -.BR shmget () -returns the identifier of the System\ V shared memory segment -associated with the value of the argument -.IR key . -It may be used either to obtain the identifier of a previously created -shared memory segment (when -.I shmflg -is zero and -.I key -does not have the value -.BR IPC_PRIVATE ), -or to create a new set. -.P -A new shared memory segment, with size equal to the value of -.I size -rounded up to a multiple of -.BR PAGE_SIZE , -is created if -.I key -has the value -.B IPC_PRIVATE -or -.I key -isn't -.BR IPC_PRIVATE , -no shared memory segment corresponding to -.I key -exists, and -.B IPC_CREAT -is specified in -.IR shmflg . -.P -If -.I shmflg -specifies both -.B IPC_CREAT -and -.B IPC_EXCL -and a shared memory segment already exists for -.IR key , -then -.BR shmget () -fails with -.I errno -set to -.BR EEXIST . -(This is analogous to the effect of the combination -.B O_CREAT | O_EXCL -for -.BR open (2).) -.P -The value -.I shmflg -is composed of: -.TP -.B IPC_CREAT -Create a new segment. -If this flag is not used, then -.BR shmget () -will find the segment associated with \fIkey\fP and check to see if -the user has permission to access the segment. -.TP -.B IPC_EXCL -This flag is used with -.B IPC_CREAT -to ensure that this call creates the segment. -If the segment already exists, the call fails. -.TP -.BR SHM_HUGETLB " (since Linux 2.6)" -Allocate the segment using "huge" pages. -See the Linux kernel source file -.I Documentation/admin\-guide/mm/hugetlbpage.rst -for further information. -.TP -.B SHM_HUGE_2MB -.TQ -.BR SHM_HUGE_1GB " (since Linux 3.8)" -.\" See https://lwn.net/Articles/533499/ -Used in conjunction with -.B SHM_HUGETLB -to select alternative hugetlb page sizes (respectively, 2\ MB and 1\ GB) -on systems that support multiple hugetlb page sizes. -.IP -More generally, the desired huge page size can be configured by encoding -the base-2 logarithm of the desired page size in the six bits at the offset -.BR SHM_HUGE_SHIFT . -Thus, the above two constants are defined as: -.IP -.in +4n -.EX -#define SHM_HUGE_2MB (21 << SHM_HUGE_SHIFT) -#define SHM_HUGE_1GB (30 << SHM_HUGE_SHIFT) -.EE -.in -.IP -For some additional details, -see the discussion of the similarly named constants in -.BR mmap (2). -.TP -.BR SHM_NORESERVE " (since Linux 2.6.15)" -This flag serves the same purpose as the -.BR mmap (2) -.B MAP_NORESERVE -flag. -Do not reserve swap space for this segment. -When swap space is reserved, one has the guarantee -that it is possible to modify the segment. -When swap space is not reserved one might get -.B SIGSEGV -upon a write -if no physical memory is available. -See also the discussion of the file -.I /proc/sys/vm/overcommit_memory -in -.BR proc (5). -.\" As at 2.6.17-rc2, this flag has no effect if SHM_HUGETLB was also -.\" specified. -.P -In addition to the above flags, the least significant 9 bits of -.I shmflg -specify the permissions granted to the owner, group, and others. -These bits have the same format, and the same -meaning, as the -.I mode -argument of -.BR open (2). -Presently, execute permissions are not used by the system. -.P -When a new shared memory segment is created, -its contents are initialized to zero values, and -its associated data structure, -.I shmid_ds -(see -.BR shmctl (2)), -is initialized as follows: -.IP \[bu] 3 -.I shm_perm.cuid -and -.I shm_perm.uid -are set to the effective user ID of the calling process. -.IP \[bu] -.I shm_perm.cgid -and -.I shm_perm.gid -are set to the effective group ID of the calling process. -.IP \[bu] -The least significant 9 bits of -.I shm_perm.mode -are set to the least significant 9 bit of -.IR shmflg . -.IP \[bu] -.I shm_segsz -is set to the value of -.IR size . -.IP \[bu] -.IR shm_lpid , -.IR shm_nattch , -.IR shm_atime , -and -.I shm_dtime -are set to 0. -.IP \[bu] -.I shm_ctime -is set to the current time. -.P -If the shared memory segment already exists, the permissions are -verified, and a check is made to see if it is marked for destruction. -.SH RETURN VALUE -On success, a valid shared memory identifier is returned. -On error, \-1 is returned, and -.I errno -is set to indicate the error. -.SH ERRORS -.TP -.B EACCES -The user does not have permission to access the -shared memory segment, and does not have the -.B CAP_IPC_OWNER -capability in the user namespace that governs its IPC namespace. -.TP -.B EEXIST -.B IPC_CREAT -and -.B IPC_EXCL -were specified in -.IR shmflg , -but a shared memory segment already exists for -.IR key . -.TP -.B EINVAL -A new segment was to be created and -.I size -is less than -.B SHMMIN -or greater than -.BR SHMMAX . -.TP -.B EINVAL -A segment for the given -.I key -exists, but \fIsize\fP is greater than the size -of that segment. -.TP -.B ENFILE -.\" [2.6.7] shmem_zero_setup()-->shmem_file_setup()-->get_empty_filp() -The system-wide limit on the total number of open files has been reached. -.TP -.B ENOENT -No segment exists for the given \fIkey\fP, and -.B IPC_CREAT -was not specified. -.TP -.B ENOMEM -No memory could be allocated for segment overhead. -.TP -.B ENOSPC -All possible shared memory IDs have been taken -.RB ( SHMMNI ), -or allocating a segment of the requested -.I size -would cause the system to exceed the system-wide limit on shared memory -.RB ( SHMALL ). -.TP -.B EPERM -The -.B SHM_HUGETLB -flag was specified, but the caller was not privileged (did not have the -.B CAP_IPC_LOCK -capability) -and is not a member of the -.I sysctl_hugetlb_shm_group -group; see the description of -.I /proc/sys/vm/sysctl_hugetlb_shm_group -in -.BR proc (5). -.SH STANDARDS -POSIX.1-2008. -.P -.B SHM_HUGETLB -and -.B SHM_NORESERVE -are Linux extensions. -.SH HISTORY -POSIX.1-2001, SVr4. -.\" SVr4 documents an additional error condition EEXIST. -.SH NOTES -.B IPC_PRIVATE -isn't a flag field but a -.I key_t -type. -If this special value is used for -.IR key , -the system call ignores all but the least significant 9 bits of -.I shmflg -and creates a new shared memory segment. -.\" -.SS Shared memory limits -The following limits on shared memory segment resources affect the -.BR shmget () -call: -.TP -.B SHMALL -System-wide limit on the total amount of shared memory, -measured in units of the system page size. -.IP -On Linux, this limit can be read and modified via -.IR /proc/sys/kernel/shmall . -Since Linux 3.16, -.\" commit 060028bac94bf60a65415d1d55a359c3a17d5c31 -the default value for this limit is: -.IP -.in +4n -.EX -ULONG_MAX - 2\[ha]24 -.EE -.in -.IP -The effect of this value -(which is suitable for both 32-bit and 64-bit systems) -is to impose no limitation on allocations. -This value, rather than -.BR ULONG_MAX , -was chosen as the default to prevent some cases where historical -applications simply raised the existing limit without first checking -its current value. -Such applications would cause the value to overflow if the limit was set at -.BR ULONG_MAX . -.IP -From Linux 2.4 up to Linux 3.15, -the default value for this limit was: -.IP -.in +4n -.EX -SHMMAX / PAGE_SIZE * (SHMMNI / 16) -.EE -.in -.IP -If -.B SHMMAX -and -.B SHMMNI -were not modified, then multiplying the result of this formula -by the page size (to get a value in bytes) yielded a value of 8\ GB -as the limit on the total memory used by all shared memory segments. -.TP -.B SHMMAX -Maximum size in bytes for a shared memory segment. -.IP -On Linux, this limit can be read and modified via -.IR /proc/sys/kernel/shmmax . -Since Linux 3.16, -.\" commit 060028bac94bf60a65415d1d55a359c3a17d5c31 -the default value for this limit is: -.IP -.in +4n -.EX -ULONG_MAX - 2\[ha]24 -.EE -.in -.IP -The effect of this value -(which is suitable for both 32-bit and 64-bit systems) -is to impose no limitation on allocations. -See the description of -.B SHMALL -for a discussion of why this default value (rather than -.BR ULONG_MAX ) -is used. -.IP -From Linux 2.2 up to Linux 3.15, the default value of -this limit was 0x2000000 (32\ MiB). -.IP -Because it is not possible to map just part of a shared memory segment, -the amount of virtual memory places another limit on the maximum size of a -usable segment: -for example, on i386 the largest segments that can be mapped have a -size of around 2.8\ GB, and on x86-64 the limit is around 127 TB. -.TP -.B SHMMIN -Minimum size in bytes for a shared memory segment: implementation -dependent (currently 1 byte, though -.B PAGE_SIZE -is the effective minimum size). -.TP -.B SHMMNI -System-wide limit on the number of shared memory segments. -In Linux 2.2, the default value for this limit was 128; -since Linux 2.4, the default value is 4096. -.IP -On Linux, this limit can be read and modified via -.IR /proc/sys/kernel/shmmni . -.\" Kernels between Linux 2.4.x and Linux 2.6.8 had an off-by-one error -.\" that meant that we could create one more segment than SHMMNI -- MTK -.\" This /proc file is not available in Linux 2.2 and earlier -- MTK -.P -The implementation has no specific limits for the per-process maximum -number of shared memory segments -.RB ( SHMSEG ). -.SS Linux notes -Until Linux 2.3.30, Linux would return -.B EIDRM -for a -.BR shmget () -on a shared memory segment scheduled for deletion. -.SH BUGS -The name choice -.B IPC_PRIVATE -was perhaps unfortunate, -.B IPC_NEW -would more clearly show its function. -.SH EXAMPLES -See -.BR shmop (2). -.SH SEE ALSO -.BR memfd_create (2), -.BR shmat (2), -.BR shmctl (2), -.BR shmdt (2), -.BR ftok (3), -.BR capabilities (7), -.BR shm_overview (7), -.BR sysvipc (7) |