𝒖𝒍𝒊𝒎𝒊𝒕 𝑼𝒏𝒓𝒂𝒗𝒆𝒍𝒆𝒅 

Soft limit – Limits the amount of resource that the process may consume. The ulimit -S command is used to view or set the soft limit. Any user can modify the soft limits.

Hard limit – It is the upper bound value to which the soft limit may be adjusted. The ulimit -H command is used to view or set the hard limit. Only the Super User can modify the hard limits.

ulimit provides a way for users to manage and control process-specific resource limits, ensuring a balance between user needs and system stability. Soft limits allow users to fine-tune resource usage, while hard limits serve as the ultimate safeguard set by the system administrator to prevent resource abuse.

ulimit is a shell built-in command, which means it is executed directly by the shell itself and not an external executable. It operates on a per-process basis, meaning the limits set by ulimit only affect the current shell session and its child processes.
( soft limits <= hard limits)

Few of the resources that can be configured using ulimit are:

Maximum Core Dump Size Limit (-c). Set to ‘unlimited’ to allow core dumps of any size. It is in blocks. (512 bytes per block)

Maximum Data Segment Size (-d). Set to ‘unlimited’ to allow programs to use as much data memory as needed. Units are in Kilobytes (KB).

Maximum File Size (-f). Set to ‘unlimited’ to allow files of any size. Measured in blocks (512 Bytes per block)

Maximum Locked-in-Memory Address Space (-l). The amount of memory a process can lock in physical RAM to prevent swapping. Set to ‘unlimited’ by default to allow locking all available memory. It is measured in KB.

Maximum Physical Memory Size (-m). Set to ‘unlimited’ to allow processes to use all available memory. Measured in KB.

Maximum Number of Open File Descriptors( -n). By default, set to a high value (1024). It is counted in number of files.

Maximum Resident Set Size (-q). Set to ‘unlimited’ by default to allow processes to use all available RAM. It is measured in KB.

Maximum Stack Size (-s). By default it is set to high value (8192KB). It is measured in KB.

Maximum CPU Time Allowed (-t). Total CPU time a process can consume. Set to ‘unlimited’ by default to use CPU time without restrictions. It is counted in seconds.

Maximum Number of User Processes (-u). Set to high value by default (2048) .It is counted in number of processes.

Maximum Virtual Memory Size (-v). Set to ‘unlimited’ by default. Counted in KB.

Maximum File Locking Count(-x). Set to high value . Counted in number of locks.

Maximum Number of Threads(-T). Set to a system-defined valye based on system configuration. It is counted in number of threads.

You can know the resources available in /etc/security/limits.conf

To Set Soft limits:

Check for current value by using anyone of the command in following way,
ulimit -t

Change it by,
ulimit -t 15

Check it by again,
ulimit -t

Use the below command in a similar way for the Hard limits.
ulimit -H -t

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An Article by: Yashwanth Naidu Tikkisetty
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