linux - Create user with partial root permissions
2014-07
Is there any way to create a user with partial root permissions on a GNU/Linux system?
For example: A user who can use the useradd
and userdel
tools, but nothing else besides regular user permissions. (Don't ask me why, I'm just curious as to if it's possible at all.)
If you use sudo
, you can specify by-command rights to users :
As an example, adding this line in your sudoers
file :
bob localhost=/sbin/halt
Will grant user bob
the right to run halt
on local system via sudo halt
, but no other right.
For more informations about sudoers
syntax, you can take a look to its man page.
I just noticed on my Ubuntu machine (ext3 filesystem) that removing write permissions from a file does not keep root from writing to it.
Is this a general rule of UNIX file permissions? Or specific to Ubuntu? Or a misconfiguration on my machine?
# touch abc # chmod ugo-w abc # python Python 2.6.4 (r264:75706, Dec 7 2009, 18:45:15) [GCC 4.4.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> open('abc','w').write('AAA\n') >>> # cat abc AAA
Writing to the file fails (as expected) if I do this from my normal user account.
Is this normal behavior?
Is there a way to prevent root from accidentally writing to a file? (Preferably using normal filesystem mechanisms, not AppArmor, etc.)
Please teach me about something that I most definitely don't understand.
NOTE: I understand that root has total control over the system and can, eg, change the permissions on any file. My question is whether currently set permissions are enforced on code running as root. The idea is the root user preventing her/himself from accidentally writing to a file.
NOTE: I also understand that one should not be logged in as root for normal operations. I just noticed this behavior and am asking you about it.
1) This is a normal behaviour. root has rw access on all files at all times.
2) You can protect a file even from root (not deliberate action, but accidental, anyway) by using
chattr +i filename.ext
That is "change attributes add immutable". To remove the protection:
chattr -i filename.ext
have a look at man chattr
for more info
Yes, this is normal. Root is god.
Yes, there are ways to prevent root from overwriting files.
- Set the immutable bit with
chattr
(+i
sets,-i
unsets). Requires root access, works only on ext2/ext3 (presumably ext4 too), but is otherwise practical. - Don't run apps as root. No root privs, no overwriting files. Use
sudo
to access system functions. - Unmount the filesystem. No mounted fs, no overwriting files. [*]
- Turn off computer. No electricity, no overwriting files.
- Set the immutable bit with
These methods follow logically from #1. As you can see, the last two methods are generally not useful, in the same way that protecting Windows against viruses by unplugging the network is generally not useful. This is why root is dangerous.[+]
[*] Discounting the possibility of "accidentally" writing directly to the block device, of course. Yes, root can do that. Yes, you can prevent that: disconnect the device.
[+] This is also where those BOfH myths come from. They're not all myths.
I think that as long as root is the superuser, and he can do anything, you cannot remove him any permission, also if you are the root. It is supposed to be the will of the root to prevent himself of doing or not an operation (such as write into a file, or open an application).
So no, chances are you would only deactivate the root account, to prevent a bad use of it.
Regards
[note to self: ye shall be humble...maybe ye are wrong]
You can also restrict file access for the root user, by using Linux kernel "Capabilities": http://www.securityfocus.com/infocus/1400
There is also the possibility of using SE-Linux or some other kernel patch to make some files immutable even to root.