Linux Permissions


Every directory or file in the Linux file system contains settings for who can read, write or execute the file. These settings are called permissions. Each file or directory is assigned to a specific user and group.

Permissions

Each file or directory has 3 security groups

  • Owner (Each file or directory has a specific owner or creator)
  • Group Access (Each file or directory is assigned to a specific group)
  • All Others (If a user is not the owner or is not assigned to the group, they are considered in the other category)

Each security group has 3 flags that control the access status

  • Flag 1 = read
  • Flag 2 = write
  • Flag 3 = execute(pertains to shell scripts or execute programs only)They are listed as ‘rwx‘ or a “” if the access is turned off.

To view the permissions, you use the ls -l command. For each file or directory listed, you will see the permissions, owner and group name, and file or directory name.

Examples What it means
-rwxrwxrwx read, write and executable for owner, group and all others
-rwxrwx— read, write and executable for owner, group only
-rwx—— read, write and executable for owner only
-rw-rw-rw read and write for owner, group and all others
-rwxr-xr-x read, write and executable by owner, only read and executable by group and others
-rw-r–r- read and write by owner, read only for group and all others

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chmod – Changing Permissions

To change the permissions, the command chmod is used.

Options What it does
u, g, o or all Whose permission you are changing: user, group, other or all
+ or>- Type of change: add permission or subtract permission
combination of r , w or x which permission you are changing: read, write or execute
file or directory name of file or directory to change
Examples What it does
chmod go-w thisfile remove write access for group and others for the file ‘thisfile’
chmod go+rw file1 file2 add read and write access for group and others for files ‘file1’ and ‘file2’
chmod ugo+rwx file1 add read, write and execute for everyone for ‘file1’.

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chown – Changing Owner

To change the owner of a file or directory, the command chown is used.

Command: chown username <file or directory>

Example: To change the owner of ‘file1’ and ‘file2’ to the user ‘roger’

chown roger file1 file2

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chgrp – Changing Group

To change the group of a file or directory, the command ‘chgrp’ is used.

Command: chgrp

Example: To change the group of ‘file1’ and ‘file2’ to the group ‘mgmt’
chgrp mgmt file1 file2

Copy from http://www.ahinc.com

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By dbglory Posted in Linux

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