NAME
getrlimit, setrlimit, prlimit - get/set resource limits SYNOPSIS
#include
#include
int getrlimit(int resource, struct rlimit *rlim); int setrlimit(int resource, const struct rlimit *rlim); int prlimit(pidt pid, int resource, const struct rlimit *newlimit, struct rlimit *oldlimit); Feature Test Macro Requirements for glibc (see featuretestmacros(7)): prlimit(): GNUSOURCE && FILEOFFSETBITS == 64 DESCRIPTION The getrlimit() and setrlimit() system calls get and set resource lim‐ its respectively. Each resource has an associated soft and hard limit, as defined by the rlimit structure: struct rlimit { rlimt rlimcur; /* Soft limit */ rlimt rlimmax; /* Hard limit (ceiling for rlimcur) */ }; The soft limit is the value that the kernel enforces for the corre‐ sponding 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 CAPSYSRESOURCE capability) may make arbitrary changes to either limit value. The value RLIMINFINITY denotes no limit on a resource (both in the structure returned by getrlimit() and in the structure passed to setr‐ limit()). The resource argument must be one of: RLIMITAS The maximum size of the process's virtual memory (address space) in bytes. This limit affects calls to brk(2), mmap(2) and mremap(2), which fail with the error ENOMEM upon exceeding this limit. Also automatic stack expansion will fail (and generate a SIGSEGV that kills the process if no alternate stack has been made available via sigaltstack(2)). Since the value is a long, on machines with a 32-bit long either this limit is at most 2 GiB, or this resource is unlimited. RLIMITCORE Maximum size of core file. When 0 no core dump files are cre‐ ated. When nonzero, larger dumps are truncated to this size. RLIMITCPU CPU time limit in seconds. When the process reaches the soft limit, it is sent a 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 SIGXCPU once per second until the hard limit is reached, at which time it is sent SIGKILL. (This latter point describes Linux behavior. Implementations vary in how they treat pro‐ cesses which continue to consume CPU time after reaching the soft limit. Portable applications that need to catch this sig‐ nal should perform an orderly termination upon first receipt of SIGXCPU.) RLIMITDATA The maximum size of the process's data segment (initialized data, uninitialized data, and heap). This limit affects calls to brk(2) and sbrk(2), which fail with the error ENOMEM upon encountering the soft limit of this resource. RLIMITFSIZE The maximum size of files that the process may create. Attempts to extend a file beyond this limit result in delivery of a 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., write(2), truncate(2)) fails with the error EFBIG. RLIMITLOCKS (Early Linux 2.4 only) A limit on the combined number of flock(2) locks and fcntl(2) leases that this process may establish. RLIMITMEMLOCK The maximum number of bytes of memory that may be locked into RAM. In effect this limit is rounded down to the nearest multi‐ ple of the system page size. This limit affects mlock(2) and mlockall(2) and the mmap(2) MAPLOCKED operation. Since Linux 2.6.9 it also affects the shmctl(2) SHMLOCK operation, where it sets a maximum on the total bytes in shared memory segments (see shmget(2)) that may be locked by the real user ID of the calling process. The shmctl(2) SHMLOCK locks are accounted for sepa‐
rately from the per-process memory locks established by mlock(2), mlockall(2), and mmap(2) MAPLOCKED; 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. RLIMITMSGQUEUE (Since Linux 2.6.8) Specifies the 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 mqopen(3). Each message queue that the user creates counts (until it is removed) against this limit according to the formula: bytes = attr.mqmaxmsg * sizeof(struct msgmsg *) + attr.mqmaxmsg * attr.mqmsgsize where attr is the mqattr structure specified as the fourth argument to mqopen(3). The first addend in the formula, which includes sizeof(struct msgmsg *) (4 bytes on Linux/i386), ensures that the user cannot
create an unlimited number of zero-length messages (such mes‐ sages nevertheless each consume some system memory for bookkeep‐ ing overhead). RLIMITNICE (since Linux 2.6.12, but see BUGS below) Specifies a ceiling to which the process's nice value can be raised using setpriority(2) or nice(2). The actual ceiling for
the nice value is calculated as 20 - rlimcur. (This strange‐ ness occurs because negative numbers cannot be specified as resource limit values, since they typically have special mean‐
ings. For example, RLIMINFINITY typically is the same as -1.) RLIMITNOFILE Specifies a value one greater than the maximum file descriptor number that can be opened by this process. Attempts (open(2), pipe(2), dup(2), etc.) to exceed this limit yield the error EMFILE. (Historically, this limit was named RLIMITOFILE on BSD.) RLIMITNPROC 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, fork(2) fails with the error EAGAIN. RLIMITRSS Specifies the limit (in pages) of 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 madvise(2) specifying MADVWILLNEED. RLIMITRTPRIO (Since Linux 2.6.12, but see BUGS)
Specifies a ceiling on the real-time priority that may be set for this process using schedsetscheduler(2) and schedset‐ param(2). RLIMITRTTIME (Since Linux 2.6.25) Specifies 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 schedyield(2). Upon reaching the soft limit, the process is sent a SIGXCPU sig‐ nal. If the process catches or ignores this signal and contin‐ ues consuming CPU time, then SIGXCPU will be generated once each second until the hard limit is reached, at which point the process is sent a SIGKILL signal.
The intended use of this limit is to stop a runaway real-time process from locking up the system. RLIMITSIGPENDING (Since Linux 2.6.8) Specifies the 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 sigqueue(3); it is always possible to use kill(2) to queue one instance of any of the signals that are not already queued to the process. RLIMITSTACK The maximum size of the process stack, in bytes. Upon reaching this limit, a SIGSEGV signal is generated. To handle this sig‐ nal, a process must employ an alternate signal stack (sigalt‐ stack(2)). Since Linux 2.6.23, this limit also determines the amount of
space used for the process's command-line arguments and environ‐ ment variables; for details, see execve(2). prlimit()
The Linux-specific prlimit() system call combines and extends the func‐ tionality of setrlimit() and getrlimit(). It can be used to both set and get the resource limits of an arbitrary process. The resource argument has the same meaning as for setrlimit() and getr‐ limit(). If the newlimit argument is a not NULL, then the rlimit structure to which it points is used to set new values for the soft and hard limits for resource. If the oldlimit argument is a not NULL, then a success‐ ful call to prlimit() places the previous soft and hard limits for resource in the rlimit structure pointed to by oldlimit. The pid argument specifies the ID of the process on which the call is to operate. If 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 CAPSYSRESOURCE capability, or the real, effective, and saved set user IDs of the target process must match the real user ID of the caller and the real, effective, and saved set group IDs of the tar‐ get process must match the real group ID of the caller. RETURN VALUE
On success, these system calls return 0. On error, -1 is returned, and errno is set appropriately. ERRORS EFAULT A pointer argument points to a location outside the accessible address space. EINVAL The value specified in resource is not valid; or, for setr‐
limit() or prlimit(): rlim->rlimcur was greater than
rlim->rlimmax. EPERM An unprivileged process tried to raise the hard limit; the CAPSYSRESOURCE capability is required to do this. Or, the caller tried to increase the hard RLIMITNOFILE limit above the current kernel maximum (NROPEN). Or, the calling process did not have permission to set limits for the process specified by pid. ESRCH Could not find a process with the ID specified in pid. VERSIONS The prlimit() system call is available since Linux 2.6.36. Library support is available since glibc 2.13. CONFORMING TO
getrlimit(), setrlimit(): SVr4, 4.3BSD, POSIX.1-2001.
prlimit(): Linux-specific. RLIMITMEMLOCK and RLIMITNPROC derive from BSD and are not specified
in POSIX.1-2001; they are present on the BSDs and Linux, but on few other implementations. RLIMITRSS derives from BSD and is not speci‐
fied in POSIX.1-2001; it is nevertheless present on most implementa‐ tions. RLIMITMSGQUEUE, RLIMITNICE, RLIMITRTPRIO, RLIMITRTTIME, and
RLIMITSIGPENDING are Linux-specific. NOTES A child process created via fork(2) inherits its parent's resource lim‐ its. Resource limits are preserved across execve(2).
One can set the resource limits of the shell using the built-in ulimit command (limit in 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 /proc/[pid]/limits; see proc(5). Ancient systems provided a vlimit() function with a similar purpose to setrlimit(). For backward compatibility, glibc also provides vlimit(). All new applications should be written using setrlimit(). BUGS In older Linux kernels, the SIGXCPU and SIGKILL signals delivered when a process encountered the soft and hard RLIMITCPU limits were deliv‐ ered 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 RLIMITCPU limit of 0 is wrongly treated as "no limit" (like RLIMINFINITY). Since Linux 2.6.17, set‐ ting a limit of 0 does have an effect, but is actually treated as a limit of 1 second. A kernel bug means that RLIMITRTPRIO 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 getpriority(2) and RLIMITNICE. This had the effect that the actual ceiling for the nice value was calculated as
19 - rlimcur. This was fixed in kernel 2.6.13. Since Linux 2.6.12, if a process reaches its soft RLIMITCPU limit and has a handler installed for 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 do not change the RLIMITCPU soft limit in this manner, and the Linux behavior is probably not standards conformant;
portable applications should avoid relying on this Linux-specific
behavior. The Linux-specific RLIMITRTTIME limit exhibits the same behavior when the soft limit is encountered. Kernels before 2.4.22 did not diagnose the error EINVAL for setrlimit()
when rlim->rlimcur was greater than rlim->rlimmax. EXAMPLE The program below demonstrates the use of prlimit().
#define GNUSOURCE
#define FILEOFFSETBITS 64
#include
#include
#include
#include
#include
#define errExit(msg) do { perror(msg); exit(EXITFAILURE); \ } while (0) int main(int argc, char *argv[]) { struct rlimit old, new; struct rlimit *newp; pidt pid; if (!(argc == 2 || argc == 4)) {
fprintf(stderr, "Usage: %s
[ " "
]\n", argv[0]); exit(EXITFAILURE); } pid = atoi(argv[1]); /* PID of target process */ newp = NULL; if (argc == 4) { new.rlimcur = atoi(argv[2]); new.rlimmax = atoi(argv[3]); newp = &new; } /* Set CPU time limit of target process; retrieve and display previous limit */ if (prlimit(pid, RLIMITCPU, newp, &old) == -1)
errExit("prlimit-1");
printf("Previous limits: soft=%lld; hard=%lld\n", (long long) old.rlimcur, (long long) old.rlimmax); /* Retrieve and display new CPU time limit */
if (prlimit(pid, RLIMITCPU, NULL, &old) == -1)
errExit("prlimit-2");
printf("New limits: soft=%lld; hard=%lld\n", (long long) old.rlimcur, (long long) old.rlimmax); exit(EXITFAILURE); } SEE ALSO prlimit(1), dup(2), fcntl(2), fork(2), getrusage(2), mlock(2), mmap(2), open(2), quotactl(2), sbrk(2), shmctl(2), malloc(3), sigqueue(3), ulimit(3), core(5), capabilities(7), signal(7) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2013-02-11 GETRLIMIT(2)