container/docs/ulimits.md

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

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

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

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

Set soft and hard limits independently:

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

Set multiple limits by repeating the flag:

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

Use unlimited for no limit:

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

% 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
...