prlimit(1)

prlimit(1) is a new util that will be available in util-linux-2.21 (now -rc1). This new util is very nice and flexible command line interface to prlimit(2) Linux syscall (supported since Linux 2.6.36).

prlimit(1) allows to get or set one or more process resource limits for given PID. When a command is given instead of PID, prlimit(1) will run this command with the given resources.

The output is flexible like output from lsblk(8) or findmnt(8). You can define the output columns, use parsable output etc.

See the default output:

  $ prlimit --pid $$
  RESOURCE   DESCRIPTION                             SOFT      HARD UNITS
  AS         address space limit                unlimited unlimited bytes
  CORE       max core file size                         0 unlimited blocks
  CPU        CPU time                           unlimited unlimited seconds
  DATA       max data size                      unlimited unlimited bytes
  FSIZE      max file size                      unlimited unlimited blocks
  LOCKS      max number of file locks held      unlimited unlimited
  MEMLOCK    max locked-in-memory address space     65536     65536 bytes
  MSGQUEUE   max bytes in POSIX mqueues            819200    819200 bytes
  NICE       max nice prio allowed to raise             0         0
  NOFILE     max number of open files                1024      4096
  NPROC      max number of processes                 1024     62809
  RSS        max resident set size              unlimited unlimited pages
  RTPRIO     max real-time priority                     0         0
  RTTIME     timeout for real-time tasks        unlimited unlimited microsecs
  SIGPENDING max number of pending signals          62809     62809
  STACK      max stack size                       8388608 unlimited bytes

or redefine the output and ask for max number of open files only:

  $ prlimit  --nofile --output RESOURCE,SOFT,HARD --pid $$
  RESOURCE SOFT HARD
  NOFILE   1024 4096

and now let's modify the soft limit of maximal core file size and maximal number of open files:

  $ prlimit --core=1000000: --nofile=100: --pid $$

the notation used for the limits is:

  soft:hard    specify both limits
  soft:        specify only the soft limit
  :hard        specify only the hard limit
  value        specify both soft and hard limits to the same value

and check the result:

  $ prlimit  --nofile --core --pid $$
  RESOURCE DESCRIPTION                 SOFT      HARD UNITS
  NOFILE   max number of open files     100      1024
  CORE     max core file size       1000000 unlimited blocks

and revert the core file soft limit:

  $ prlimit --core=unlimited: --pid $$

  $ prlimit --core --pid $$
  RESOURCE DESCRIPTION             SOFT      HARD UNITS
  CORE     max core file size unlimited unlimited blocks

Do you want to restrict CPU time for given command (sort(1) in this example):

   $ prlimit --cpu=10 sort -u hugefile

I think prlimit(1) is much better than the shell built-in command ulimit.

Thanks to Davidlohr Bueso who found time to implement prlimit(1) for util-linux 2.21.

-- In memory of Dennis M. Ritchie