ulimits

tags : Linux

What is it? §

• A shell builtin that works on a per-process basis. Limit is then adopted by the shell that called it and inherited by children(i.e children will have their own limits, number will be same though).
• The shell builtin essentially wraps getrlimit / setrlimit system calls.
• Option in container tools like docker, podman. i.e it’ll set ulimit for the container sort of.
  • TODO: ulimit in containers is tricky, I’ve to check it properly when I get time. I mean it’s used slightly differently and nproc has some host specific things etc. Little complicated.

What about process? §

• Once a process starts, its ulimits are set. The process itself can change its soft ulimit up to the hard ulimit.
• prlimit can help you change ulimits of running process

Relationship w limits.conf §

Limits are a property of a process.

About limits.conf §

• The file does not affect system services.
• /etc/security/limits.conf file provides configuration for the pam_limits PAM module
• /etc/security/limits.conf allows setting resource limits for users and groups logged in via PAM.
• However /etc/security/limits.conf does not work for the system using systemd. Following needs to be changed instead.
  • /etc/systemd/system.conf
  • /etc/systemd/user.conf
  • /etc/systemd/system/unit.d/override.conf

Types of limits §

• Hard limits
  • Set by root and enforced by the kernel.
  • Mark the maximum value which cannot be exceeded by setting a soft limit.
• Soft limits
  • Configured by the user within the range allowed by the hard limits.
  • Simply the currently enforced limits.

System and User limits §

Limits are inherited when a child process is created

• System wide limits
  • Should be set during the system initialization in init scripts, systemd specific conf files etc.
• User limits
  • Should be set during user login for example by using pam_limits (/etc/security/limits.conf)