Resource limits (ulimits)

Set per-process resource limits for your containers.

Overview

The --ulimit option of container run (and container create) sets Linux resource limits (rlimits) for the container's init process.

Syntax

bash

container run --ulimit <type>=<soft>[:<hard>] ...

If you set a single value, it applies as both soft and hard limit:

bash

container run --ulimit nofile=65536 -it ubuntu:24.04 bash

Set soft and hard limits independently:

bash

container run --ulimit nofile=65536:131072 -it ubuntu:24.04 bash

Set multiple limits by repeating the flag:

bash

container run --ulimit nofile=65536:131072 --ulimit cpu=60 -it ubuntu:24.04 bash

Use unlimited for no limit:

bash

container run --ulimit nproc=unlimited -it ubuntu:24.04 bash

[!NOTE] nofile=unlimited reliably fails to start the container (NSPOSIXErrorDomain Code=1 "Operation not permitted"). This isn't a container bug — unlimited sets both soft and hard limits to UINT64_MAX, and Linux caps RLIMIT_NOFILE's hard limit at the guest's /proc/sys/fs/nr_open (1048576 here); anything above that ceiling fails the same way, unlimited included. Use an explicit value at or below nr_open instead, e.g. nofile=1048576.

Supported limit types

Type	Maps to	Description
`core`	`RLIMIT_CORE`	Maximum core file size, in bytes
`cpu`	`RLIMIT_CPU`	Maximum CPU time, in seconds
`data`	`RLIMIT_DATA`	Maximum data segment size, in bytes
`fsize`	`RLIMIT_FSIZE`	Maximum file size, in bytes
`locks`	`RLIMIT_LOCKS`	Maximum number of file locks
`memlock`	`RLIMIT_MEMLOCK`	Maximum amount of memory that may be locked into RAM
`msgqueue`	`RLIMIT_MSGQUEUE`	Maximum bytes in POSIX message queues
`nice`	`RLIMIT_NICE`	Maximum nice priority
`nofile`	`RLIMIT_NOFILE`	Maximum number of open file descriptors
`nproc`	`RLIMIT_NPROC`	Maximum number of processes
`rss`	`RLIMIT_RSS`	Maximum resident set size, in bytes
`rtprio`	`RLIMIT_RTPRIO`	Maximum real-time priority
`rttime`	`RLIMIT_RTTIME`	Maximum real-time CPU time, in microseconds
`sigpending`	`RLIMIT_SIGPENDING`	Maximum number of pending signals
`stack`	`RLIMIT_STACK`	Maximum stack size, in bytes

Inspect limits inside a container

console

% container run -it --rm ubuntu:24.04 bash -c "ulimit -a"
open files                          (-n) 1048576
cpu time                   (seconds, -t) unlimited
...
% container run --ulimit nofile=131072 --ulimit cpu=60 -it --rm ubuntu:24.04 bash -c "ulimit -a"
open files                          (-n) 131072
cpu time                   (seconds, -t) 60
...