How do I make a File “unalterable” (write protect) such as it cannot be changed or deleted even by root or superuser under Apple OS X UNIX operating systems?
You can make a file unalterable i.e write protect it but root / superuser can always make changes using the same method. In other words, you can not write protect your stuff from root. Linux use can use the chattr command for write protecting the files.
Change File Flags With the chflags Command
The chflags command modifies the file flags. First, open the terminal and to set system immutable flag type the following command:
sudo chflags schg fileName |
The owner can set the user immutable flag as follows (no need to use sudo or superuser password):
chflags uchg fileName |
In this, example set user immutable flag on resume.txt file, enter:
chflags uchg resume.txt |
To list flags, enter:
ls -lO resume.txt |
Sample outputs:
-rw-r--r-- 1 vivek wheel uchg 18424 Jun 2 18:48 resume.txt
Now, try deleting or writing to the same file, enter:
rm resume.txt
Sample outputs:
override rw-r--r-- vivek/wheel uchg for resume.txt? y rm: resume.txt: Operation not permitted
How Do I Remove User Immutable Flag?
Use the command as follows:
chflags nouchg resume.txt ls -lO resume.txt |
Sample outputs:
-rw-r--r-- 1 vivek wheel - 18424 Jun 2 18:48 resume.txt
Putting the letters no before causes the flag to be cleared.
How Do I Remove System Immutable Flag?
Use the command as follows:
sudo chflags noschg resume.txt ls -lO resume.txt< |
Please note that above commands works on both the file and folder (remember, under UNIX everything is file).
Finder GUI Tool Method
Right click or control+click (command + I does the same thing) the file or folder you want to write protect and select Get Info. You will get info window as follows:
Click a small lock icon (located at bottom right) and provide your admin password. Once authenticated click on “Locked” check box to lock the file (this is same as running the above chflags command). Additionally, you can add or remove user write permission too.
Recommend Readings:
For more information on use of the chflags utility and additional options, please refer to the chflags man page, viewable by typing man chflags from the command line:
man chflags
4 comment
See if there is a chattr command; if so then this will work:
chattr +i somefile
But be warned; root, unless he is a noob, can do anything…
Typo here:
supruser => superuser
As always, thanks for pointing it out.
Don’t forget the good old chmod program. There’s a mathematical formula for determining permissions as well.
4 is read, 2 is write and 1 is execute for all three groups; Owner, Group, World.
to set the permissions for read write, and execute is 4+2+1=7 by the owner. For Read and write by group is 4+2=6. To be readable to the world is 4.
This would be represented in the file list ( ls -al ) as:
d rwx rw- r- –
The ‘d’ is a special flag often called the sticky bit. In this case, it’s indicating the entry is a directory. To safely ( and properly ) set these permissions you would enter it as;
chmod 0764
Wildcards like * and ? are accepted here.
This will allow members of the same group mess with each others files. To restrict access to everyone by the owner would be;
chmod 0744
to recurse the folders beyond ( supposing it’s a folder ) add a -R to the command.
and whenever in doubt, “man chmod” or “man chgrp” or “man chown”.
Hope this helps.
– Dan.