Chmod Command【转】

Source:http://www.thegeekstuff.com/2010/06/chmod-command-examples

Following are the symbolic representation of three different roles:

u is for user, g is for group, and o is for others.

Following are the symbolic representation of three different permissions:

r is for read permission, w is for write permission, x is for execute permission.

Following are few examples on how to use the symbolic representation on chmod.

Add single permission to a file/directory

Changing permission to a single set. + symbol means adding permission. For example, do the following to give execute permission for the user irrespective of anything else:

$ chmod u+x filename

Add multiple permission to a file/directory

Use comma to separate the multiple permission sets as shown below.

$ chmod u+r,g+x filename

Remove permission from a file/directory

Following example removes read and write permission for the user.

$ chmod u-rx filename

Change permission for all roles on a file/directory

Following example assigns execute privilege to user, group and others (basically anybody can execute this file).
$ chmod a+x filename

Make permission for a file same as another file (using reference)

If you want to change a file permission same as another file, use the reference option as shown below. In this example, file2’s permission will be set exactly same as file1’s permission.

$ chmod --reference=file1 file2

Apply the permission to all the files under a directory recursively

Use option -R to change the permission recursively as shown below.

$ chmod -R 755 directory-name/

( 命令格式：chmod abc file
其中a,b,c各为一个八进制数字，分别表示User、Group、及Other的权限。
4 (100) 表示可读。
2 (010) 表示可写。
1 (001) 表示可执行。
若要rwx属性则4+2+1=7；
若要rw-属性则4+2=6；
若要r-x属性则4+1=5。

    例如：# chmod a+rx filename 
            让所有用户可以读和执行文件filename。 
          # chmod go-rx filename 
            取消同组和其他用户的读和执行文件filename的权限。 
          # chmod 741 filename 
            让本人可读写执行、同组用户可读、其他用户可执行文件filename。 
          # chmod -R 755 /home/oracle 
            递归更改目录权限，本人可读写执行、同组用户可读可执行、其他用户可读可执行)

Change execute permission only on the directories (files are not affected)

On a particular directory if you have multiple sub-directories and files, the following command will assign execute permission only to all the sub-directories in the current directory (not the files in the current directory).

$ chmod u+X *
Note: If the files has execute permission already for either the group or others, the above command will assign the execute permission to the user