My posts about issues concerning Linux OS and network administration

Ulimit settings

User limits – limit the use of system-wide resources.

Syntax
      ulimit [-acdfHlmnpsStuv] [limit]

Options

   -S   Change and report the soft limit associated with a resource. 
   -H   Change and report the hard limit associated with a resource. 

   -a   All current limits are reported. 
   -c   The maximum size of core files created. 
   -d   The maximum size of a process's data segment. 
   -f   The maximum size of files created by the shell(default option) 
   -l   The maximum size that may be locked into memory. 
   -m   The maximum resident set size. 
   -n   The maximum number of open file descriptors. 
   -p   The pipe buffer size. 
   -s   The maximum stack size. 
   -t   The maximum amount of cpu time in seconds. 
   -u   The maximum number of processes available to a single user. 
   -v   The maximum amount of virtual memory available to the process.

Ulimit provides control over the resources available to the shell and to processes started by it. There are two types of limits: hard limits, soft limits.

The soft limit is the value that the kernel enforces for the corresponding resource while the hard limit acts as a ceiling for the soft limit. An unprivileged process may only set its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit. A privileged process may make arbitrary changes to either limit value.

If limit is given, it is the new value of the specified resource. Otherwise, the current value of the soft limit for the specified resource is printed, unless the `-H’ option is supplied.

When setting new limits, if neither `-H’ nor `-S’ is supplied, both the hard and soft limits are set.

Restricting per user processes ( -u) can be useful for limiting the potential effects of a fork bomb.

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.

The return status is zero unless an invalid option is supplied, a non-numeric argument other than unlimited is supplied as a limit, or an error occurs while setting a new limit.


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