Certain resources in Unix systems can be limited to ensure that the most important processes have enough resources.
The ulimit is a build-in bash command that can limit the use of system-wide resources. The ulimit -a lists
all current resource limits.
The command response unlimited means that the current user can consume all the resources the current system supports.
Limits:
- soft:
- the value that the kernel enforces for the corresponding resource
- the value in the range from 0 to hard limit
- changes can be made by both unprivileged and privileged process
- hard:
- acts as a ceiling for the soft limit
- changes can be only made by a privileged process
The changes made with ulimit only affect the current shell. To make permanent changes
the /etc/security/limits.conf needs to be modified.
Examples:
Keys for individual resources are displayed in an orange rectangle on the image above.
Show limits for open files:
1# Hard limits
2lukash@ubuntu:~$ ulimit -H -n
31048576
4#Soft limits
5lukash@ubuntu:~$ ulimit -S -n
61024
Change soft limits for open files:
1lukash@ubuntu:~$ ulimit -S -n 2048
2lukash@ubuntu:~$ ulimit -S -n
32048
Values are in 1024-byte increments, except for -t, which is in seconds, -p, which is in units of 512-byte blocks,
and -n and -u, which are unscaled values.