Linux: File Permissions - Revision history

Michael: /* Default Permissions and Umask */

2013-08-15T19:46:09Z

Default Permissions and Umask

Michael at 19:21, 15 August 2013

2013-08-15T19:21:02Z

Michael: /* Special Permissions */

2013-08-15T19:06:35Z

Special Permissions

Michael: Created page with "== Checking File Permissions == The 'ls -l' command can be used to check the current permissions on a file. [michael@head ~]$ ls -l boston_ping.sh -rwxr-xr-x. 1 micha..."

2013-08-15T19:06:21Z

Created page with "== Checking File Permissions == The 'ls -l' command can be used to check the current permissions on a file. <syntaxhighlight> [michael@head ~]$ ls -l boston_ping.sh -rwxr-xr-x. 1 micha..."

New page

== Checking File Permissions ==

The 'ls -l' command can be used to check the current permissions on a file.

<syntaxhighlight>
[michael@head ~]$ ls -l boston_ping.sh
-rwxr-xr-x. 1 michael michael 2199 Jul 3 08:59 boston_ping.sh
</syntaxhighlight>

The permissions are shown in the left hand column.

The first bit shows the type of file: - = Directory, d = directory, b = device, l = linked file

The next nine bits represent the file permissions.

The last bit may be a '.' showing that the file is under the control of SELinux. A '+' would show that it is under the control of SELinux and and Access Control List (ACL).

== File Permissions ==

File permissions in Linux are divided into three groups: Users, Groups and Others. Each Group can have Read Write and Execute Permissions.

The file shown above has execute permissions for all groups, read permissions for the user and group, and write permissions only for the user.

== Special Permissions ==

There are three special permissions: SUID, SGID and the Sticky Bit.

The SUID and SGID allow the file to be executed by others with the authority of the owner. An example of this is the passwd command.

<syntaxhighlight>
ls - l /usr/bin/passwd
-rwsr-xr-x 1 root root 32200 Jan 28 2010 /usr/bin/passwd
</syntaxhighlight>

The sticky but is shown in the execubte bit of the permissions such as the /tmp folder. The Sticky bit allow file to be copied to the directory while retaining ownership.

<syntaxhighlight>
drwxrwxrwt. 31 root root 57344 Aug 15 20:09 tmp
</syntaxhighlight>

← Older revision		Revision as of 19:46, 15 August 2013
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	A umask of 0022 would give 777 - 022 = 755 permissions. But once the execute permission are removed this gives 644.		A umask of 0022 would give 777 - 022 = 755 permissions. But once the execute permission are removed this gives 644.
		+
		+
		+	The exception to this is default permissions on a directory. This must have execute permissions in order to allow sub files to be accessed.

	== Changing Permissions ==		== Changing Permissions ==

← Older revision		Revision as of 19:06, 15 August 2013
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	The SUID and SGID allow the file to be executed by others with the authority of the owner. An example of this is the passwd command.		The SUID and SGID allow the file to be executed by others with the authority of the owner. An example of this is the passwd command.
−

	<syntaxhighlight>		<syntaxhighlight>

@@ Line 15: / Line 15: @@
 The last bit may be a '.' showing that the file is under the control of SELinux.  A '+'  would show that it is under the control of SELinux and and Access Control List (ACL).
 == File Permissions ==
@@ Line 23: / Line 21: @@
 The file shown above has execute permissions for all groups, read permissions for the user and group, and write permissions only for the user.
 == Special Permissions ==
@@ Line 39: / Line 41: @@
 <syntaxhighlight>
 drwxrwxrwt.  31 root root 57344 Aug 15 20:09 tmp
 </syntaxhighlight>