| GETRLIMIT(2) | Linux Programmer's Manual | GETRLIMIT(2) |
getrlimit, setrlimit, prlimit - get/set resource limits
#include <sys/time.h>
#include <sys/resource.h>
int getrlimit(int resource, struct rlimit
*rlim);
int setrlimit(int resource, const struct rlimit
*rlim);
int prlimit(pid_t pid, int
resource, const struct rlimit *new_limit,
struct rlimit *old_limit);
prlimit(): _GNU_SOURCE
The getrlimit() and setrlimit() system calls get and set resource limits. Each resource has an associated soft and hard limit, as defined by the rlimit structure:
struct rlimit {
rlim_t rlim_cur; /* Soft limit */
rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
};
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 CAP_SYS_RESOURCE capability in the initial user namespace) may make arbitrary changes to either limit value.
The value RLIM_INFINITY denotes no limit on a resource (both in the structure returned by getrlimit() and in the structure passed to setrlimit()).
The resource argument must be one of:
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 */
bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
/* For overhead */
attr.mq_maxmsg * attr.mq_msgsize;
/* For message data */
The Linux-specific prlimit() system call combines and extends the functionality 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 getrlimit().
If the new_limit 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 old_limit argument is a not NULL, then a successful call to prlimit() places the previous soft and hard limits for resource in the rlimit structure pointed to by old_limit.
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 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 and the real, effective, and saved set group IDs of the target process must match the real group ID of the caller.
On success, these system calls return 0. On error, -1 is returned, and errno is set appropriately.
The prlimit() system call is available since Linux 2.6.36. Library support is available since glibc 2.13.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| getrlimit (), setrlimit (), prlimit () | Thread safety | MT-Safe |
getrlimit(), setrlimit(): POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
prlimit(): Linux-specific.
RLIMIT_MEMLOCK and 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. RLIMIT_RSS derives from BSD and is not specified in POSIX.1; it is nevertheless present on most implementations. RLIMIT_MSGQUEUE, RLIMIT_NICE, RLIMIT_RTPRIO, RLIMIT_RTTIME, and RLIMIT_SIGPENDING are Linux-specific.
A child process created via fork(2) inherits its parent's resource limits. Resource limits are preserved across execve(2).
Resource limits are per-process attributes that are shared by all of the threads in a process.
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 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().
Since version 2.13, the glibc getrlimit() and setrlimit() wrapper functions no longer invoke the corresponding system calls, but instead employ prlimit(), for the reasons described in BUGS.
The name of the glibc wrapper function is prlimit(); the underlying system call is prlimit64().
In older Linux kernels, the SIGXCPU and SIGKILL signals delivered when a process encountered the soft and hard 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 RLIMIT_CPU limit of 0 is wrongly treated as "no limit" (like 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.
A kernel bug means that 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 getpriority(2) and RLIMIT_NICE. This had the effect that the actual ceiling for the nice value was calculated as 19 - rlim_cur. This was fixed in kernel 2.6.13.
Since Linux 2.6.12, if a process reaches its soft RLIMIT_CPU 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 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. The Linux-specific RLIMIT_RTTIME 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->rlim_cur was greater than rlim->rlim_max.
Linux doesn't return an error when an attempt to set RLIMIT_CPU has failed, for compatibility reasons.
The glibc getrlimit() and setrlimit() wrapper functions use a 64-bit rlim_t data type, even on 32-bit platforms. However, the rlim_t data type used in the getrlimit() and setrlimit() system calls is a (32-bit) unsigned long. Furthermore, in Linux, the kernel represents resource limits on 32-bit platforms as unsigned long. However, a 32-bit data type is not wide enough. The most pertinent limit here is 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—that is, as wide as a 64-bit off_t (assuming a program compiled with _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 unsigned long, then the glibc setrlimit() wrapper function silently converted the limit value to RLIM_INFINITY. In other words, the requested resource limit setting was silently ignored.
Since version 2.13, glibc works around the limitations of the getrlimit() and setrlimit() system calls by implementing setrlimit() and getrlimit() as wrapper functions that call prlimit().
The program below demonstrates the use of prlimit().
#define _GNU_SOURCE
#define _FILE_OFFSET_BITS 64
#include <stdint.h>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/resource.h>
#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 <pid> [<new-soft-limit> "
"<new-hard-limit>]\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=%jd; hard=%jd\n",
(intmax_t) old.rlim_cur, (intmax_t) 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=%jd; hard=%jd\n",
(intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
exit(EXIT_SUCCESS);
}
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), cgroups(7), credentials(7), signal(7)
This page is part of release 5.10 of the Linux 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/.
| 2020-11-01 | Linux |