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Permissions and attributes

command what it means what it does how to use it
chmod change modifiers edits the permissions of a file chmod +x filename
chattr change attributes edits the attributes of a file chattr +i filename

chmod is used to edit the permissions on a file. There are 3 permissions and 3 groups, for a total of 9 permissions. The permissions are:

  • read - allows the group to read the file
  • write - allows the group to edit the file
  • execute - allows the group to run the file as a program

for example when using ls -la you see all of the files permissions

user
 |   group
 |  /   
 |  |  others
 |  |  |
-rw-r--r-- 1 username groupname  264 Sep 24 19:08 more instructions.md

so this file the owner has rw, the group has r and everyone has r

to make a file executable for all users you would run the following command

chmod a+x filename

character group name who it applies to
u user the owner of the file
g group users who are members of the files' group
o others users not included in u or g
a all u, g and o

chmod can take either a set of three octal (base 8) numbers to set the permissions across all groups, or list the groups "a+" and the permissions that you want to add or "a-" and the permissions you want to subtract.

The character representations of the permissions are:

letter number binary permission
r 4 100 read
w 2 010 write
x 1 001 execute

So chmod a+rwx filename is the same as chmod 777 filename

how to run a program