Linux File Permissions

	Text	Binary	Directory
Read	cat <file>	cp /bin/ls	ls
Write	cat > <file>	cc a.c	rm <directory>
eXecute	./<file>	ls	cd <directory>

 

Only 2 users can change the permissions of a file

• the Owner
• super user or root

ls -l
Owner-Group-Others HardLinks username groupName bytes date filename

drwxrwxr-x 2 trainee trainee 4096 Jun 14 15:03 as
-rw-rw-r-- 1 trainee trainee    0 Jun 14 14:27 f2
-rw-rw-r-- 1 trainee trainee  148 Jun 14 14:28 f3
-rw-rw-r-- 1 trainee trainee  148 Jun 14 14:28 f4
-rw-rw-r-- 1 trainee trainee  888 Jun 14 14:29 f5
-rw-rw-r-- 1 trainee trainee    0 Jun 14 15:10 fruits
-rw-rw-r-- 1 trainee trainee    0 Jun 14 15:10 g1
-rw-rw-r-- 1 trainee trainee    0 Jun 14 15:10 g2

Change permissions on a file

• Numerical: use chmod 777 filename all permissions to a file.
• Symbolic: use chmod a+x,g-w <filename>    [User Group] [+/-] [r/w/x]

UMASK:

• specifies what has to be denied
• its only for newly created files

you can find out umask by typing umask

[trainee@localhost purna]$ umask
0002 the last three specify what permission to deny to the owner group and others