Ulimit and free commands

Ulimit is an internal key function in Linux. It has a set of parameters used to set limits on the usage of shell processes generated by it and their sub-processes.

Ulimit Command Format: ulimit [Options] [limit]
1. ulimit parameter description

Option [Options]	Description	Example
-H	Set hard resource limits. Once set, they cannot be added.	Ulimit-HS 64; hard resources are restricted. The thread stack size is 64 KB.
-S	Set soft resource limit. After setting, you can add but cannot exceed the hard resource setting.	Ulimit-Sn 32; restrict soft resources and 32 file descriptors.
-	Displays all current limit information.	Ulimit-A; displays all current limit information.
-C	The maximum core file size, in blocks.	Ulimit-C unlimited; the size of the generated core file is not limited.
-D	The maximum data segment size of a process, in Kbytes.	Ulimit-D Unlimited; do not limit the Data Segment Size of the process.
-F	Maximum number of files that can be created by a process, in blocks.	Ulimit-F 2048; restrict the maximum file size that can be created by a process to 2048 blocks.
-L	Maximum lockable memory size, in Kbytes.	Ulimit-l 32; the maximum lockable memory size is 32 Kbytes.
-M	The maximum memory size, in Kbytes.	Ulimit-M unlimited; maximum memory is not limited.
-N	Maximum number of file descriptors that can be opened.	Ulimit-N 128; a maximum of 128 file descriptors can be used.
-P	The size of the MPs queue buffer, in Kbytes.	Ulimit-P 512; limit the MPs queue buffer size to 512 Kbytes.
-S	Thread stack size, in Kbytes.	Ulimit-s 512; limits the thread stack size to 512 Kbytes.
-T	The maximum CPU usage time, in seconds.	Ulimit-T unlimited; the maximum CPU usage time is not limited.
-U	Maximum number of processes available to users.	Ulimit-u 64; limit that users can use up to 64 processes.
-V	Maximum available virtual memory of a process, in Kbytes.	Ulimit-V 200000; Limit the maximum available virtual memory to 200000 Kbytes.

The free command displays the idle and used memory of the system.

Command Format: Free [-B |-k |-M |-G]

Parameters:

-B: displays the memory in bytes.

-G: Display memory in GB bytes

-K displays memory in K bytes

-M: Display memory in MB bytes

-T shows the total number of columns in a row.