Modification of file access permissions in Unix operating systems

Article Title: Modification of file access permissions in Unix operating systems. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

In a Unix operating system, you can use the chmod command to modify the file access permission. The format of the chmod command is as follows:

　Format 1: chmod symbolic_mode file...

Format 2: chmod absolute_mode file...

Format 1: symbolic_mode. The command format of the symbolic mode is as follows:

Chmod [who] op permision file...

The who item indicates the user type, and its content is one or more of the following:

U file owner)

G User group)

O others (other)

A all)

Op indicates action:

+ Indicates adding the permission specified by permission.

-Cancels the permission specified by permission.

A permission item is an access permission with one or more of the following content:

R indicates readable

W indicates writable

X indicates executable

Example:

The chmod u + w test report owner is "writable" to the test and report files"

The chmod u-x abc. c owner cannot execute the abc. c file.

Chmod u + rwx myfile1 owner for myfile1 "readable, writable, and executable"

Chmod ugo + rwx myfile2 anyone on myfile1 "readable, writable, and executable"

Format 2: absolute mode (absolute_mode). The command format of symbolic mode is as follows:

Chmod xyz file...

X, y, and z are numbers 0-7 respectively, indicating the access permissions of the owner, user group, and others to the file. The values of x, y, and z are:

A * 4 + B * 2 + c

Where,

A = 1 indicates readable, and a = 0 indicates unreadable;

B = 1 indicates writable, and B = 0 indicates non-writable;

C = 1 indicates executable, and c = 0 indicates not executable;

Example:

Chmod 751 ncp owners have all the rights to "read, write, and execute" to ncp; members in the group have only the "readable and executable" rights to ncp; other users have only "executable" rights to ncp.