Use of chown chmod usermod command

Source: Internet
Author: User

I. CHOWN command

Purpose: Change the owner or group of a file. The command is composed of the word change owner.

Example:

1. Change the file owner:

Chown Jim program. c

The owner of the file program. C is changed to Jim. As the owner, Jim can use the CHMOD command to allow or deny other users access to program. C.

2. Change the directory owner:

Chown-r JOHN: build/tmp/src

Change the owner and group of all files in the/tmp/src directory to user John and group build

-R recursively changes the owner of all subdirectories and files under a specified directory.

-V: displays the work done by the CHOWN command.

Ii. chmod command

Purpose: Change the access permission of a file or directory.

This command has two usage methods:
One is the text setting method that contains letters and operator expressions, and the other is the number setting method that contains numbers.

1. text setting

Chmod [who] [+ |-| =] [mode] File Name

The meaning of each option in the command is:

The operator who is one of the following letters or their combination:

U indicates "user", that is, the owner of a file or directory.

G indicates "group users", that is, all users with the same group ID as the file owner.

O indicates "Other (Others) Users ".

A Indicates "All (all) Users ". It is the default value of the system.

The operation symbol can be:

+ Add a permission.

-Cancel a permission.

= Grant the given permission and cancel all other permissions (if any ).

Set the permissions indicated by mode to any combination of the following letters:

R readable.

W writable.

X executable.

X adds the X attribute only when the target file is executable to some users or the target file is a directory.

S sets the owner or group ID of the process to the file owner during file execution. In the format of "U + S" to set the user ID of the file, and "G + S" to set the group ID.

T save the program text to the swap device.

U has the same permissions as the file owner.

G. users in the same group have the same permissions as file owners.

O has the same permissions as other users.

File Name: list of files separated by spaces to change permissions. Wildcards are supported.

Multiple permission methods can be provided in a command line, separated by commas. Example: chmod g + R, O + r example

Grant the same group and other users the permission to read the file example.

2. digit setting

First, we must understand the meaning of the property represented by numbers: 0 indicates no permission, 1 indicates executable permission, 2 indicates writable permission, 4 indicates readable permission, and then add it.

Therefore, the format of the numeric attribute should be three Octal numbers from 0 to 7. The order is (u) (g) (o ).

For example, if you want the owner of a file to have the "read/write" permission, you need to set 4 (readable) + 2 (writable) to 6 (read/write ).

The number setting method is generally in the following format:

Chmod [mode] File Name

The chmod command can be used in two ways. One is the text setting method that contains letters and operator expressions, and the other is the number setting method that contains numbers.
1. text setting method
Chmod [who] [+ |-| =] [mode] File Name

The meaning of each option in the command is:
The operator who is one of the following letters or their combination:
U indicates "user", that is, the owner of a file or directory.
G indicates "group users", that is, all users with the same group ID as the file owner.
O indicates "Other (Others) Users ".
A Indicates "All (all) Users ". It is the default value of the system.

The operation symbol can be:
+ Add a permission.
-Cancel a permission.
= Grant the given permission and cancel all other permissions (if any ).

Set the permissions indicated by mode to any combination of the following letters:
R readable.
W writable.
X executable.
X adds the X attribute only when the target file is executable to some users or the target file is a directory.
S sets the owner or group ID of the process to the file owner during file execution. In the format of "U + S" to set the user ID of the file, and "G + S" to set the group ID.
T save the program text to the swap device.
U has the same permissions as the file owner.
G. users in the same group have the same permissions as file owners.
O has the same permissions as other users.

File Name: list of files separated by spaces to change permissions. Wildcards are supported.

Multiple permission methods can be provided in a command line, separated by commas. Example: chmod g + R, O + r example

Grant the same group and other users the permission to read the file example.

2. Number setting method

First, we must understand the meaning of the property represented by numbers: 0 indicates no permission, 1 indicates executable permission, 2 indicates writable permission, 4 indicates readable permission, and then add it. Therefore, the format of the numeric attribute should be three Octal numbers from 0 to 7. The order is (u) (g) (o ).

For example, if you want the owner of a file to have the "read/write" permission, you need to set 4 (readable) + 2 (writable) to 6 (read/write ).

The number setting method is generally in the following format:

Chmod [mode] File Name

Example:
(1) text setting method:
Example 1: $ chmod A + x sort
That is, set the property of the file sort:
File owner (u) adds execution permission
Add execution permission for users in the same group as the file owner (g)
Other users (o) add execution Permissions

Example 2: $ chmod ug + W, o-x text
That is, set the text attribute of the file:
Add write permission to file owner (u)
Add write permission for users in the same group as the file owner (g)
Other users (o) delete execution Permissions

Example 3: $ chmod U + s a. Out
Assume that the permission for a. out after chmod is executed is (you can use the LS-l a. out command to view the permission ):
-RWS -- X 1 inin users 7192 Nov 4 14:22 A. Out
In addition, this execution file uses a text file shiyan1.c with the "-RW -------" access permission, that is, only the owner of the file has the read and write permissions.

When other users execute. when the program is out, his identity is changed to inin (because the s option is used in the CHMOD command) for the moment ), therefore, he can read the shiyan1.c file (although this file is set to be inaccessible to others), which is the function of S.

Therefore, in the entire system, especially the root itself, it is best not to set too many files of this type (unless necessary) to ensure system security, avoid system intrusion due to bugs in some programs.

Example 4: $ chmod A-x mm.txt
$ Chmod-x mm.txt
$ Chmod Ugo-x mm.txt

The preceding three commands Delete the execution permission of the mm.txt file, and set the object to all users.

(2) number setting method:
Example 1: $ chmod 644 mm.txt
$ LS-l
Set the attributes of the file mm.txt:
-RW-r -- 1 inin users 1155 Nov 5 mm.txt
File owner (u) inin has read and write permissions
Users in the same group as the file owner (g) have read permission
Others (o) have read permission

Example 2: $ chmod 750 wch.txt
$ LS-l
-Rwxr-x --- 1 inin users 44137 Nov 12 9:22 wchtxt
That is, set the properties of the wchtxt file:
File owner (u) inin readable/writable/executable
Readable/executable permission of persons in the same group as the file owner
Others (o) do not have any Permissions

CHOWN command

Function: Modify the owner and group of a file or directory. This command is also very common. For example, if the root user copies a file to Xu, the root user should set the owner of the file to Xu to allow Xu to access the file. Otherwise, user Xu cannot access this file.

Syntax: chown [Option] user or group file

Note: chown will change the owner of a specified file to a specified user or group. Users can be user names or user IDs. A group can be a group name or group ID. Files are separated by spaces to change the permission list. Wildcards are supported.

The options of this command are as follows:
-R recursively changes the owner of all subdirectories and files under a specified directory.
-V: displays the work done by the CHOWN command.

Example 1: Change the owner of the Shiyan. c file to Wang.
$ Chown Wang Shiyan. c

Example 2: Change the owner of the directory/his and all files and subdirectories to Wang and the group to users.
$ Chown-r Wang. Users/his

3. usermod command
Function Description: modifies user account groups and logon directories.
Syntax: usermod [-lu] [-C <remarks>] [-D <logon directory>] [-E <validity period>] [-F <buffer days>] [-G <group>] [-G <group>] [-L <Account Name>] [-S] [-u] [User Account]

Note: usermod can be used to modify user account settings.

Parameters:
-C <remarks> modify the remarks of the user account.
-D logon directory> modify the directory when a user logs in.
-E <validity period> modifies the validity period of an account.
-F <buffer days> change the number of days after the password expires to close the account.
-G <group>: Modify the group to which the user belongs.
-G <group> modify the additional group to which the user belongs.
-L <Account Name> modify the user account name.
-L lock the user password to make it invalid.
-S: Modify the shell used after user login.
-U: Modify the user ID.
-U unlocks the password.

 

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