# getrlimit

## NAME



           getrlimit, setrlimit, prlimit - get/set resource limits
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#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 *_Nullable** _new_limit_**,**
                       **struct rlimit *_Nullable** _old_limit_**);**
    
           **struct rlimit {**
               **rlim_t  rlim_cur;** /* Soft limit */
               **rlim_t  rlim_max;** /* Hard limit (ceiling for rlim_cur) */
           **};**
    
           **typedef** /* ... */  **rlim_t;** /* Unsigned integer type */
    
       Feature Test Macro Requirements for glibc (see
       feature_test_macros(7)):
    
           **prlimit**():
               _GNU_SOURCE
    


## DESCRIPTION



           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.
    
           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:
    
           **RLIMIT_AS**
                  This is the maximum size of the process's virtual memory
                  (address space).  The limit is specified in bytes, and is
                  rounded down to the system page size.  This limit affects
                  calls to brk(2), mmap(2), and mremap(2), which fail with
                  the error **ENOMEM** upon exceeding this limit.  In addition,
                  automatic stack expansion fails (and generates 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.
    
           **RLIMIT_CORE**
                  This is the maximum size of a _core_ file (see core(5)) in
                  bytes that the process may dump.  When 0 no core dump files
                  are created.  When nonzero, larger dumps are truncated to
                  this size.
    
           **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 **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 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
                  **SIGXCPU**.)
    
           **RLIMIT_DATA**
                  This is the maximum size of the process's data segment
                  (initialized data, uninitialized data, and heap).  The
                  limit is specified in bytes, and is rounded down to the
                  system page size.  This limit affects calls to brk(2),
                  sbrk(2), and (since Linux 4.7) mmap(2), which fail with the
                  error **ENOMEM** upon encountering the soft limit of this
                  resource.
    
           **RLIMIT_FSIZE**
                  This is the maximum size in bytes 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**.
    
           **RLIMIT_LOCKS**(Linux 2.4.0 to Linux 2.4.24)
                  This is a limit on the combined number of flock(2) locks
                  and fcntl(2) leases that this process may establish.
    
           **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 mlock(2), mlockall(2), and the mmap(2) **MAP_LOCKED**
                  operation.  Since Linux 2.6.9, it also affects the
                  shmctl(2) **SHM_LOCK** 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) **SHM_LOCK** locks are accounted for
                  separately from the per-process memory locks established by
                  mlock(2), mlockall(2), and mmap(2) **MAP_LOCKED** ; a process
                  can lock bytes up to this limit in each of these two
                  categories.
    
                  Before Linux 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.
    
           **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
                  mq_open(3).  Each message queue that the user creates
                  counts (until it is removed) against this limit according
                  to the formula:
    
                      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 */
    
                  where _attr_ is the _mq_attr_ structure specified as the fourth
                  argument to mq_open(3), and the _msg_msg_ and
                  _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).
    
           **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 setpriority(2) or nice(2).  The actual
                  ceiling for the nice value is calculated as _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, **RLIM_INFINITY** typically is the same
                  as -1.  For more detail on the nice value, see sched(7).
    
           **RLIMIT_NOFILE**
                  This 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 **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 **CAP_SYS_RESOURCE** capability) may have "in
                  flight" to other processes, by being passed across UNIX
                  domain sockets.  This limit applies to the sendmsg(2)
                  system call.  For further details, see unix(7).
    
           **RLIMIT_NPROC**
                  This is a limit on the number of extant process (or, more
                  precisely on Linux, threads) for the real user ID of the
                  calling process.  So long as the current number of
                  processes belonging to this process's real user ID is
                  greater than or equal to this limit, fork(2) fails with the
                  error **EAGAIN**.
    
                  The **RLIMIT_NPROC** limit is not enforced for processes that
                  have either the **CAP_SYS_ADMIN** or the **CAP_SYS_RESOURCE**
                  capability, or run with real user ID 0.
    
           **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 madvise(2) specifying **MADV_WILLNEED**.
    
           **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 sched_setscheduler(2) and
                  sched_setparam(2).
    
                  For further details on real-time scheduling policies, see
                  sched(7)
    
           **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 sched_yield(2).
    
                  Upon reaching the soft limit, the process is sent a **SIGXCPU**
                  signal.  If the process catches or ignores this signal and
                  continues 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.
    
                  For further details on real-time scheduling policies, see
                  sched(7)
    
           **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 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.
    
           **RLIMIT_STACK**
                  This is the maximum size of the process stack, in bytes.
                  Upon reaching this limit, a **SIGSEGV** signal is generated.
                  To handle this signal, a process must employ an alternate
                  signal stack (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 execve(2).
    
       **prlimit()**
           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 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 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.
    


## RETURN VALUE



           On success, these system calls return 0.  On error, -1 is
           returned, and _errno_ is set to indicate the error.
    


## 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
                  **setrlimit**() or **prlimit**(): _rlim- >rlim_cur_ was greater than
                  _rlim- >rlim_max_.
    
           **EPERM** An unprivileged process tried to raise the hard limit; the
                  **CAP_SYS_RESOURCE** capability is required to do this.
    
           **EPERM** The caller tried to increase the hard **RLIMIT_NOFILE** limit
                  above the maximum defined by _/proc/sys/fs/nr_open_ (see
                  proc(5))
    
           **EPERM**(**prlimit**()) 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_.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────────┬───────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────────┼───────────────┼─────────┤
           │ **getrlimit**(), **setrlimit**(), **prlimit**()  │ Thread safety │ MT-Safe │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## STANDARDS



           **getrlimit**()
           **setrlimit**()
                  POSIX.1-2008.
    
           **prlimit**()
                  Linux.
    
           **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.
    


## NOTES



           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**().
    
       **C library/kernel ABI differences**
           Since glibc 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**().
    


## BUGS



           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 Linux 2.6.8.
    
           In Linux 2.6.x kernels before Linux 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 Linux
           2.6.12; the problem is fixed in Linux 2.6.13.
    
           In Linux 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 Linux 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 Linux 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.
    
       **Representation of "large" resource limit values on 32-bit platforms**
           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 glibc 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**().
    


## EXAMPLES



           The program below demonstrates the use of **prlimit**().
    
           #define _GNU_SOURCE
           #define _FILE_OFFSET_BITS 64
           #include <err.h>
           #include <stdint.h>
           #include <stdio.h>
           #include <stdlib.h>
           #include <sys/resource.h>
           #include <time.h>
    
           int
           main(int argc, char *argv[])
           {
               pid_t          pid;
               struct rlimit  old, new;
               struct rlimit  *newp;
    
               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)
                   err(EXIT_FAILURE, "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)
                   err(EXIT_FAILURE, "prlimit-2");
               printf("New limits: soft=%jd; hard=%jd\n",
                      (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max);
    
               exit(EXIT_SUCCESS);
           }
    


* * *