.\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992 .\" and Copyright (c) 2002, 2004, 2005, 2008, 2010 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" Modified by Michael Haardt .\" Modified 1993-07-23 by Rik Faith .\" Modified 1996-01-13 by Arnt Gulbrandsen .\" Modified 1996-01-22 by aeb, following a remark by .\" Tigran Aivazian .\" Modified 1996-04-14 by aeb, following a remark by .\" Robert Bihlmeyer .\" Modified 1996-10-22 by Eric S. Raymond .\" Modified 2001-05-04 by aeb, following a remark by .\" Håvard Lygre .\" Modified 2001-04-17 by Michael Kerrisk .\" Modified 2002-06-13 by Michael Kerrisk .\" Added note on nonstandard behavior when SIGCHLD is ignored. .\" Modified 2002-07-09 by Michael Kerrisk .\" Enhanced descriptions of 'resource' values .\" Modified 2003-11-28 by aeb, added RLIMIT_CORE .\" Modified 2004-03-26 by aeb, added RLIMIT_AS .\" Modified 2004-06-16 by Michael Kerrisk .\" Added notes on CAP_SYS_RESOURCE .\" .\" 2004-11-16 -- mtk: the getrlimit.2 page, which formally included .\" coverage of getrusage(2), has been split, so that the latter .\" is now covered in its own getrusage.2. .\" .\" Modified 2004-11-16, mtk: A few other minor changes .\" Modified 2004-11-23, mtk .\" Added notes on RLIMIT_MEMLOCK, RLIMIT_NPROC, and RLIMIT_RSS .\" to "CONFORMING TO" .\" Modified 2004-11-25, mtk .\" Rewrote discussion on RLIMIT_MEMLOCK to incorporate kernel .\" 2.6.9 changes. .\" Added note on RLIMIT_CPU error in older kernels .\" 2004-11-03, mtk, Added RLIMIT_SIGPENDING .\" 2005-07-13, mtk, documented RLIMIT_MSGQUEUE limit. .\" 2005-07-28, mtk, Added descriptions of RLIMIT_NICE and RLIMIT_RTPRIO .\" 2008-05-07, mtk / Peter Zijlstra, Added description of RLIMIT_RTTIME .\" 2010-11-06, mtk: Added documentation of prlimit() .\" .TH GETRLIMIT 2 2017-03-13 "Linux" "Linux Programmer's Manual" .SH NAME getrlimit, setrlimit, prlimit \- get/set resource limits .SH SYNOPSIS .B #include .br .B #include .sp .BI "int getrlimit(int " resource ", struct rlimit *" rlim ); .br .BI "int setrlimit(int " resource ", const struct rlimit *" rlim ); .sp .BI "int prlimit(pid_t " pid ", int " resource \ ", const struct rlimit *" new_limit , .br .BI " struct rlimit *" old_limit ); .sp .in -4n Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .sp .BR prlimit (): _GNU_SOURCE .SH DESCRIPTION The .BR getrlimit () and .BR setrlimit () system calls get and set resource limits respectively. Each resource has an associated soft and hard limit, as defined by the .I rlimit structure: .PP .in +4n .nf struct rlimit { rlim_t rlim_cur; /* Soft limit */ rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */ }; .fi .in The soft limit is the value that the kernel enforces for the corresponding resource. The hard limit acts as a ceiling for the soft limit: an unprivileged process may set only its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit. A privileged process (under Linux: one with the .B CAP_SYS_RESOURCE capability) may make arbitrary changes to either limit value. .PP The value .B RLIM_INFINITY denotes no limit on a resource (both in the structure returned by .BR getrlimit () and in the structure passed to .BR setrlimit ()). .PP The .I resource argument must be one of: .TP .B RLIMIT_AS This is the maximum size of the process's virtual memory (address space) in bytes. .\" since 2.0.27 / 2.1.12 This limit affects calls to .BR brk (2), .BR mmap (2), and .BR mremap (2), which fail with the error .B ENOMEM upon exceeding this limit. Also automatic stack expansion will fail (and generate a .B SIGSEGV that kills the process if no alternate stack has been made available via .BR sigaltstack (2)). Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP either this limit is at most 2 GiB, or this resource is unlimited. .TP .B RLIMIT_CORE This is the maximum size of a .I core file (see .BR core (5)) that the process may dump. When 0 no core dump files are created. When nonzero, larger dumps are truncated to this size. .TP .B RLIMIT_CPU This is a limit, in seconds, on the amount of CPU time that the process can consume. When the process reaches the soft limit, it is sent a .B SIGXCPU signal. The default action for this signal is to terminate the process. However, the signal can be caught, and the handler can return control to the main program. If the process continues to consume CPU time, it will be sent .B SIGXCPU once per second until the hard limit is reached, at which time it is sent .BR SIGKILL . (This latter point describes Linux behavior. Implementations vary in how they treat processes which continue to consume CPU time after reaching the soft limit. Portable applications that need to catch this signal should perform an orderly termination upon first receipt of .BR SIGXCPU .) .TP .B RLIMIT_DATA This is the maximum size of the process's data segment (initialized data, uninitialized data, and heap). This limit affects calls to .BR brk (2) and .BR sbrk (2), which fail with the error .B ENOMEM upon encountering the soft limit of this resource. .TP .B RLIMIT_FSIZE This is the maximum size of files that the process may create. Attempts to extend a file beyond this limit result in delivery of a .B SIGXFSZ signal. By default, this signal terminates a process, but a process can catch this signal instead, in which case the relevant system call (e.g., .BR write (2), .BR truncate (2)) fails with the error .BR EFBIG . .TP .BR RLIMIT_LOCKS " (early Linux 2.4 only)" .\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65 This is a limit on the combined number of .BR flock (2) locks and .BR fcntl (2) leases that this process may establish. .TP .B RLIMIT_MEMLOCK This is the maximum number of bytes of memory that may be locked into RAM. This limit is in effect rounded down to the nearest multiple of the system page size. This limit affects .BR mlock (2), .BR mlockall (2), and the .BR mmap (2) .B MAP_LOCKED operation. Since Linux 2.6.9, it also affects the .BR shmctl (2) .B SHM_LOCK operation, where it sets a maximum on the total bytes in shared memory segments (see .BR shmget (2)) that may be locked by the real user ID of the calling process. The .BR shmctl (2) .B SHM_LOCK locks are accounted for separately from the per-process memory locks established by .BR mlock (2), .BR mlockall (2), and .BR mmap (2) .BR MAP_LOCKED ; a process can lock bytes up to this limit in each of these two categories. In Linux kernels before 2.6.9, this limit controlled the amount of memory that could be locked by a privileged process. Since Linux 2.6.9, no limits are placed on the amount of memory that a privileged process may lock, and this limit instead governs the amount of memory that an unprivileged process may lock. .TP .BR RLIMIT_MSGQUEUE " (since Linux 2.6.8)" This is a limit on the number of bytes that can be allocated for POSIX message queues for the real user ID of the calling process. This limit is enforced for .BR mq_open (3). Each message queue that the user creates counts (until it is removed) against this limit according to the formula: .nf Since Linux 3.5: bytes = attr.mq_maxmsg * sizeof(struct msg_msg) + min(attr.mq_maxmsg, MQ_PRIO_MAX) * sizeof(struct posix_msg_tree_node)+ /* For overhead */ attr.mq_maxmsg * attr.mq_msgsize; /* For message data */ Linux 3.4 and earlier: bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) + /* For overhead */ attr.mq_maxmsg * attr.mq_msgsize; /* For message data */ .fi where .I attr is the .I mq_attr structure specified as the fourth argument to .BR mq_open (3), and the .I msg_msg and .I posix_msg_tree_node structures are kernel-internal structures. The "overhead" addend in the formula accounts for overhead bytes required by the implementation and ensures that the user cannot create an unlimited number of zero-length messages (such messages nevertheless each consume some system memory for bookkeeping overhead). .TP .BR RLIMIT_NICE " (since Linux 2.6.12, but see BUGS below)" This specifies a ceiling to which the process's nice value can be raised using .BR setpriority (2) or .BR nice (2). The actual ceiling for the nice value is calculated as .IR "20\ \-\ rlim_cur" . The useful range for this limit is thus from 1 (corresponding to a nice value of 19) to 40 (corresponding to a nice value of -20). This unusual choice of range was necessary because negative numbers cannot be specified as resource limit values, since they typically have special meanings. For example, .B RLIM_INFINITY typically is the same as \-1. For more detail on the nice value, see .BR sched (7). .TP .B RLIMIT_NOFILE This specifies a value one greater than the maximum file descriptor number that can be opened by this process. Attempts .RB ( open (2), .BR pipe (2), .BR dup (2), etc.) to exceed this limit yield the error .BR EMFILE . (Historically, this limit was named .B RLIMIT_OFILE on BSD.) Since Linux 4.5, this limit also defines the maximum number of file descriptors that an unprivileged process (one without the .BR CAP_SYS_RESOURCE capability) may have "in flight" to other processes, by being passed across UNIX domain sockets. This limit applies to the .BR sendmsg (2) system call. For further details, see .BR unix (7). .TP .B RLIMIT_NPROC This is the maximum number of processes (or, more precisely on Linux, threads) that can be created for the real user ID of the calling process. Upon encountering this limit, .BR fork (2) fails with the error .BR EAGAIN . This limit is not enforced for processes that have either the .B CAP_SYS_ADMIN or the .B CAP_SYS_RESOURCE capability. .TP .B RLIMIT_RSS This is a limit (in bytes) on the process's resident set (the number of virtual pages resident in RAM). This limit has effect only in Linux 2.4.x, x < 30, and there affects only calls to .BR madvise (2) specifying .BR MADV_WILLNEED . .\" As at kernel 2.6.12, this limit still does nothing in 2.6 though .\" talk of making it do something has surfaced from time to time in LKML .\" -- MTK, Jul 05 .TP .BR RLIMIT_RTPRIO " (since Linux 2.6.12, but see BUGS)" This specifies a ceiling on the real-time priority that may be set for this process using .BR sched_setscheduler (2) and .BR sched_setparam (2). For further details on real-time scheduling policies, see .BR sched (7) .TP .BR RLIMIT_RTTIME " (since Linux 2.6.25)" This is a limit (in microseconds) on the amount of CPU time that a process scheduled under a real-time scheduling policy may consume without making a blocking system call. For the purpose of this limit, each time a process makes a blocking system call, the count of its consumed CPU time is reset to zero. The CPU time count is not reset if the process continues trying to use the CPU but is preempted, its time slice expires, or it calls .BR sched_yield (2). Upon reaching the soft limit, the process is sent a .B SIGXCPU signal. If the process catches or ignores this signal and continues consuming CPU time, then .B SIGXCPU will be generated once each second until the hard limit is reached, at which point the process is sent a .B SIGKILL signal. The intended use of this limit is to stop a runaway real-time process from locking up the system. For further details on real-time scheduling policies, see .BR sched (7) .TP .BR RLIMIT_SIGPENDING " (since Linux 2.6.8)" This is a limit on the number of signals that may be queued for the real user ID of the calling process. Both standard and real-time signals are counted for the purpose of checking this limit. However, the limit is enforced only for .BR sigqueue (3); it is always possible to use .BR kill (2) to queue one instance of any of the signals that are not already queued to the process. .\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit .\" that was present in kernels <= 2.6.7. MTK Dec 04 .TP .B RLIMIT_STACK This is the maximum size of the process stack, in bytes. Upon reaching this limit, a .B SIGSEGV signal is generated. To handle this signal, a process must employ an alternate signal stack .RB ( sigaltstack (2)). Since Linux 2.6.23, this limit also determines the amount of space used for the process's command-line arguments and environment variables; for details, see .BR execve (2). .SS prlimit() .\" commit c022a0acad534fd5f5d5f17280f6d4d135e74e81 .\" Author: Jiri Slaby .\" Date: Tue May 4 18:03:50 2010 +0200 .\" .\" rlimits: implement prlimit64 syscall .\" .\" commit 6a1d5e2c85d06da35cdfd93f1a27675bfdc3ad8c .\" Author: Jiri Slaby .\" Date: Wed Mar 24 17:06:58 2010 +0100 .\" .\" rlimits: add rlimit64 structure .\" The Linux-specific .BR prlimit () system call combines and extends the functionality of .BR setrlimit () and .BR getrlimit (). It can be used to both set and get the resource limits of an arbitrary process. The .I resource argument has the same meaning as for .BR setrlimit () and .BR getrlimit (). If the .IR new_limit argument is a not NULL, then the .I rlimit structure to which it points is used to set new values for the soft and hard limits for .IR resource . If the .IR old_limit argument is a not NULL, then a successful call to .BR prlimit () places the previous soft and hard limits for .I resource in the .I rlimit structure pointed to by .IR old_limit . The .I pid argument specifies the ID of the process on which the call is to operate. If .I pid is 0, then the call applies to the calling process. To set or get the resources of a process other than itself, the caller must have the .B CAP_SYS_RESOURCE capability in the user namespace of the process whose resource limits are being changed, or the real, effective, and saved set user IDs of the target process must match the real user ID of the caller .I and the real, effective, and saved set group IDs of the target process must match the real group ID of the caller. .\" FIXME . this permission check is strange .\" Asked about this on LKML, 7 Nov 2010 .\" "Inconsistent credential checking in prlimit() syscall" .SH RETURN VALUE On success, these system calls return 0. On error, \-1 is returned, and .I errno is set appropriately. .SH ERRORS .TP .B EFAULT A pointer argument points to a location outside the accessible address space. .TP .B EINVAL The value specified in .I resource is not valid; or, for .BR setrlimit () or .BR prlimit (): .I rlim\->rlim_cur was greater than .IR rlim\->rlim_max . .TP .B EPERM An unprivileged process tried to raise the hard limit; the .B CAP_SYS_RESOURCE capability is required to do this. .TP .B EPERM The caller tried to increase the hard .B RLIMIT_NOFILE limit above the maximum defined by .IR /proc/sys/fs/nr_open (see .BR proc (5)) .TP .B EPERM .RB ( prlimit ()) The calling process did not have permission to set limits for the process specified by .IR pid . .TP .B ESRCH Could not find a process with the ID specified in .IR pid . .SH VERSIONS The .BR prlimit () system call is available since Linux 2.6.36. Library support is available since glibc 2.13. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lbw35 lb lb l l l. Interface Attribute Value T{ .BR getrlimit (), .BR setrlimit (), .BR prlimit () T} Thread safety MT-Safe .TE .SH CONFORMING TO .BR getrlimit (), .BR setrlimit (): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. .br .BR prlimit (): Linux-specific. .B RLIMIT_MEMLOCK and .B RLIMIT_NPROC derive from BSD and are not specified in POSIX.1; they are present on the BSDs and Linux, but on few other implementations. .B RLIMIT_RSS derives from BSD and is not specified in POSIX.1; it is nevertheless present on most implementations. .BR RLIMIT_MSGQUEUE , .BR RLIMIT_NICE , .BR RLIMIT_RTPRIO , .BR RLIMIT_RTTIME , and .B RLIMIT_SIGPENDING are Linux-specific. .SH NOTES A child process created via .BR fork (2) inherits its parent's resource limits. Resource limits are preserved across .BR execve (2). Lowering the soft limit for a resource below the process's current consumption of that resource will succeed (but will prevent the process from further increasing its consumption of the resource). One can set the resource limits of the shell using the built-in .IR ulimit command .RI ( limit in .BR csh (1)). The shell's resource limits are inherited by the processes that it creates to execute commands. Since Linux 2.6.24, the resource limits of any process can be inspected via .IR /proc/[pid]/limits ; see .BR proc (5). Ancient systems provided a .BR vlimit () function with a similar purpose to .BR setrlimit (). For backward compatibility, glibc also provides .BR vlimit (). All new applications should be written using .BR setrlimit (). .SS C library/ kernel ABI differences Since version 2.13, the glibc .BR getrlimit () and .BR setrlimit () wrapper functions no longer invoke the corresponding system calls, but instead employ .BR prlimit (), for the reasons described in BUGS. The name of the glibc wrapper function is .BR prlimit (); the underlying system call is .BR prlimit64 (). .SH BUGS In older Linux kernels, the .B SIGXCPU and .B SIGKILL signals delivered when a process encountered the soft and hard .B RLIMIT_CPU limits were delivered one (CPU) second later than they should have been. This was fixed in kernel 2.6.8. In 2.6.x kernels before 2.6.17, a .B RLIMIT_CPU limit of 0 is wrongly treated as "no limit" (like .BR RLIM_INFINITY ). Since Linux 2.6.17, setting a limit of 0 does have an effect, but is actually treated as a limit of 1 second. .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2 A kernel bug means that .\" See https://lwn.net/Articles/145008/ .B RLIMIT_RTPRIO does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13. In kernel 2.6.12, there was an off-by-one mismatch between the priority ranges returned by .BR getpriority (2) and .BR RLIMIT_NICE . This had the effect that the actual ceiling for the nice value was calculated as .IR "19\ \-\ rlim_cur" . This was fixed in kernel 2.6.13. .\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2 Since Linux 2.6.12, .\" The relevant patch, sent to LKML, seems to be .\" http://thread.gmane.org/gmane.linux.kernel/273462 .\" From: Roland McGrath redhat.com> .\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process .\" Date: 2005-01-23 23:27:46 GMT if a process reaches its soft .BR RLIMIT_CPU limit and has a handler installed for .BR SIGXCPU , then, in addition to invoking the signal handler, the kernel increases the soft limit by one second. This behavior repeats if the process continues to consume CPU time, until the hard limit is reached, at which point the process is killed. Other implementations .\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0 do not change the .BR RLIMIT_CPU soft limit in this manner, and the Linux behavior is probably not standards conformant; portable applications should avoid relying on this Linux-specific behavior. .\" FIXME . https://bugzilla.kernel.org/show_bug.cgi?id=50951 The Linux-specific .BR RLIMIT_RTTIME limit exhibits the same behavior when the soft limit is encountered. Kernels before 2.4.22 did not diagnose the error .B EINVAL for .BR setrlimit () when .I rlim\->rlim_cur was greater than .IR rlim\->rlim_max . .\" .SS Representation of """large""" resource limit values on 32-bit platforms The glibc .BR getrlimit () and .BR setrlimit () wrapper functions use a 64-bit .IR rlim_t data type, even on 32-bit platforms. However, the .I rlim_t data type used in the .BR getrlimit () and .BR setrlimit () system calls is a (32-bit) .IR "unsigned long" . Furthermore, in Linux versions before 2.6.36, the kernel represents resource limits on 32-bit platforms as .IR "unsigned long" . However, a 32-bit data type is not wide enough. .\" https://bugzilla.kernel.org/show_bug.cgi?id=5042 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=12201 The most pertinent limit here is .BR RLIMIT_FSIZE , which specifies the maximum size to which a file can grow: to be useful, this limit must be represented using a type that is as wide as the type used to represent file offsets\(emthat is, as wide as a 64-bit .BR off_t (assuming a program compiled with .IR _FILE_OFFSET_BITS=64 ). To work around this kernel limitation, if a program tried to set a resource limit to a value larger than can be represented in a 32-bit .IR "unsigned long" , then the glibc .BR setrlimit () wrapper function silently converted the limit value to .BR RLIM_INFINITY . In other words, the requested resource limit setting was silently ignored. This problem was addressed in Linux 2.6.36 with two principal changes: .IP * 3 the addition of a new kernel representation of resource limits that uses 64 bits, even on 32-bit platforms; .IP * the addition of the .BR prlimit () system call, which employs 64-bit values for its resource limit arguments. .PP Since version 2.13, .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=12201 glibc works around the limitations of the .BR getrlimit () and .BR setrlimit () system calls by implementing .BR setrlimit () and .BR getrlimit () as wrapper functions that call .BR prlimit (). .SH EXAMPLE The program below demonstrates the use of .BR prlimit (). .PP .nf #define _GNU_SOURCE #define _FILE_OFFSET_BITS 64 #include #include #include #include #include #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\ } while (0) int main(int argc, char *argv[]) { struct rlimit old, new; struct rlimit *newp; pid_t pid; if (!(argc == 2 || argc == 4)) { fprintf(stderr, "Usage: %s [ " "]\\n", argv[0]); exit(EXIT_FAILURE); } pid = atoi(argv[1]); /* PID of target process */ newp = NULL; if (argc == 4) { new.rlim_cur = atoi(argv[2]); new.rlim_max = atoi(argv[3]); newp = &new; } /* Set CPU time limit of target process; retrieve and display previous limit */ if (prlimit(pid, RLIMIT_CPU, newp, &old) == \-1) errExit("prlimit\-1"); printf("Previous limits: soft=%lld; hard=%lld\\n", (long long) old.rlim_cur, (long long) old.rlim_max); /* Retrieve and display new CPU time limit */ if (prlimit(pid, RLIMIT_CPU, NULL, &old) == \-1) errExit("prlimit\-2"); printf("New limits: soft=%lld; hard=%lld\\n", (long long) old.rlim_cur, (long long) old.rlim_max); exit(EXIT_SUCCESS); } .fi .SH SEE ALSO .BR prlimit (1), .BR dup (2), .BR fcntl (2), .BR fork (2), .BR getrusage (2), .BR mlock (2), .BR mmap (2), .BR open (2), .BR quotactl (2), .BR sbrk (2), .BR shmctl (2), .BR malloc (3), .BR sigqueue (3), .BR ulimit (3), .BR core (5), .BR capabilities (7), .BR cgroups (7), .BR credentials (7), .BR signal (7) .SH COLOPHON This page is part of release 4.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.