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       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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       prlimit(): _GNU_SOURCE


       The  getrlimit()  and  setrlimit()  system calls get and set resource limits respectively.
       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) 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:

              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.

              Maximum size of a core file (see core(5)).  When 0 no core dump files are  created.
              When nonzero, larger dumps are truncated to this size.

              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  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.)

              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.

              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.

       RLIMIT_LOCKS (Early Linux 2.4 only)
              A limit on the combined number of flock(2) locks  and  fcntl(2)  leases  that  this
              process may establish.

              The  maximum number of bytes of memory that may be locked into RAM.  In effect this
              limit is rounded down to the nearest multiple of the system page size.  This  limit
              affects mlock(2) and 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.  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.

       RLIMIT_MSGQUEUE (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
              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)
              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.   (This  strangeness  occurs  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.)

              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

              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.  This limit is not enforced for processes that
              have either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability.

              Specifies the limit (in bytes) 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 MADV_WILLNEED.

       RLIMIT_RTPRIO (since Linux 2.6.12, but see BUGS)
              Specifies a ceiling on the real-time priority that may  be  set  for  this  process
              using sched_setscheduler(2) and sched_setparam(2).

       RLIMIT_RTTIME (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 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.

       RLIMIT_SIGPENDING (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.

              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

       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, 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


       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.


       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).

       │InterfaceAttributeValue   │
       │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.


       A child process created via fork(2)  inherits  its  parent's  resource  limits.   Resource
       limits are preserved across 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 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 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  call
       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.

   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  versions
       before 2.6.36, 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

       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.

       This problem was addressed in Linux 2.6.36 with two principal changes:

       *  the  addition of a new kernel representation of resource limits that uses 64 bits, even
          on 32-bit platforms;

       *  the addition of the prlimit() system call, which employs 64-bit values for its resource
          limit arguments.

       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


       The program below demonstrates the use of prlimit().

       #define _GNU_SOURCE
       #define _FILE_OFFSET_BITS 64
       #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)

       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]);

           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)
           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)
           printf("New limits: soft=%lld; hard=%lld\n",
                   (long long) old.rlim_cur, (long long) old.rlim_max);



       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)


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