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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

Buy it now, or read it online on Safari Bookshelf.


sum [options] files

Calculate and print a checksum and the number of (1 KB) blocks for file. If no files are specified, or file is -, read from standard input. Useful for verifying data transmission.



The default setting. Use the BSD checksum algorithm.

-s, --sysv

Use alternate checksum algorithm as used on System V. The block size is 512 bytes.


Print a help message and then exit.


Print the version number and then exit.

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