umask permissions explanation
what is umask?
umask is the default permissions for writing a file in the system
where the settings for umask?
1 – /etc/profile
2 – /etc/bashrc
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if [ $UID -gt 199 ] && [ "`id -gn`" = "`id -un`" ]; then umask 002 else umask 022 fi |
3 – users can change umask in the fly via umask command
what is current umask value?
u can run the command “umask to get the value”
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[root@localhost ~]# umask 0022 |
first bit zero for
4000 = SUID
2000 = SGID
1000 = sticky bit
how to calculate it
first, let’s create a file with root account that has umask 0022
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[root@localhost ~]# touch test_default_umask_for_root [root@localhost ~]# ls -l test_default_umask_for_root -rw-r--r--. 1 root root 0 Jul 10 06:04 test_default_umask_for_root |
the file wrote in permission 644, and our umask value is 0022
so here how to set the correct one
first, let’s assume we want to make the default files rwrwrw 666
r = 4
w = 2
so every sector for the owner, group, others
to get the correct umask number we will say
777 – x = 666
this is equal to
777 – 666 = x
x = 111
so our umask will be 111
example
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[root@localhost ~]# umask 111 [root@localhost ~]# touch 111 [root@localhost ~]# ls -alah 111 -rw-rw-rw-. 1 root root 0 Jul 14 03:51 111 |
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002 -rw-rw-r--.drwxrwxr-x. no write for other 022 -rw-r--r--.drwxr-xr-x. no write + read + execute 027 -rw-r-----.drwxr-x---. no write + group read 077 -rw-------.drwx------. only belowngs to woner |
2 to remove the write permeation
7 to remove all permeation
0 give it all permeations actually ( don’t implement any permeation try 000 ;))
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