Linux Helper

cp Command Syntax:

The syntax is as follows to copy files and directories using the cp command:

 
cp SOURCE DEST
cp SOURCE DIRECTORY
cp SOURCE1 SOURCE2 SOURCE3 SOURCEn DIRECTORY
cp [OPTION]  SOURCE DEST
cp [OPTION]  SOURCE DIRECTORY

chmod Command Syntax:

The chmod command changes the access mode of one file or multiple files.
The syntax for the chmod command is:
chmod [option] mode files

Options:

Option	Description
-R	Descend directory arguments recursively while setting modes.
-f	Suppress error messages if command fails.

Mode:

Mode	Description
Who	u=user, g=group, o=other, a=all (default)
Opcode	+ means add permission - means remove permission = means assign permission and remove the permission of unspecified fields
Permission	r=Read, w=write, x=Execute, s=set uid bit, t=sticky bit u=user, g=group, o=other, l=mandatory locking

Examples

chmod 751 tech chmod u=rwx, g=rx, o=x tech chmod =r tech
Following are few examples on how to use the symbolic representation on chmod.

1. 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

2. Add multiple permission to a file/directory

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

$ chmod u+r,g+x filename

3. Remove permission from a file/directory

Following example removes read and write permission for the user.

$ chmod u-rx filename

4. 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

5. 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

6. 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/

7. 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