Difference between revisions of "Sudo"
Line 9: | Line 9: | ||
pkexec vim /etc/sudoers | pkexec vim /etc/sudoers | ||
</pre> | </pre> | ||
− | If that doesn't work then you'll have to resort to rebooting the machine in ''' | + | If that doesn't work then you'll have to resort to rebooting the machine in '''single user mode''' and edit /etc/sudoers as root. |
+ | |||
+ | == I keep breaking /etc/sudoers == | ||
+ | |||
+ | Something near the '''includedir''' line in your '''/etc/sudoers''' file will not parse. The problem is that you probably deleted the '''#''' character in front of the '''includedir''' directive. In this case it's supposed to resemble a preprocessor directive in '''C'''. No, it's not a comment. It looks like one and you probably thought you were uncommenting a disabled line. This was a really stupid syntax decision by the '''sudo''' designers. The directive should be '''#includedir'''. Put the '''#''' character back. And make sure there is no space between it and the include, otherwise sudo will then think it's a comment and it will ignore it. Again, stupid syntax. | ||
+ | <pre> | ||
+ | ubuntu@web1:~$ sudo ls /root | ||
+ | >>> /etc/sudoers: syntax error near line 31 <<< | ||
+ | sudo: parse error in /etc/sudoers near line 31 | ||
+ | sudo: no valid sudoers sources found, quitting | ||
+ | sudo: unable to initialize policy plugin | ||
+ | </pre> | ||
+ | |||
+ | Your '''/etc/sudoers''' file probably looks something like this: | ||
+ | <pre> | ||
+ | # User privilege specification | ||
+ | root ALL=(ALL:ALL) ALL | ||
+ | |||
+ | # Members of the admin group may gain root privileges | ||
+ | %admin ALL=(ALL) NOPASSWD:ALL | ||
+ | |||
+ | # Allow members of group sudo to execute any command | ||
+ | %sudo ALL=(ALL:ALL) ALL | ||
+ | |||
+ | # See sudoers(5) for more information on "#include" directives: | ||
+ | includedir /etc/sudoers.d | ||
+ | </pre> | ||
== NOPASSWD does not work == | == NOPASSWD does not work == |
Revision as of 09:41, 25 August 2015
Use `visudo` to make changes to /etc/sudoers.
Contents
I broke /etc/sudoers and now I can't run sudo to fix it
It's just like when you lock your keys in the car. If you have the policy kit utilities installed then you likely have a utility celled pkexec installed. This is like a lightweight sudo, sort of. So just edit your /etc/sshd-config file using pkexec and be on your way:
pkexec vim /etc/sudoers
If that doesn't work then you'll have to resort to rebooting the machine in single user mode and edit /etc/sudoers as root.
I keep breaking /etc/sudoers
Something near the includedir line in your /etc/sudoers file will not parse. The problem is that you probably deleted the # character in front of the includedir directive. In this case it's supposed to resemble a preprocessor directive in C. No, it's not a comment. It looks like one and you probably thought you were uncommenting a disabled line. This was a really stupid syntax decision by the sudo designers. The directive should be #includedir. Put the # character back. And make sure there is no space between it and the include, otherwise sudo will then think it's a comment and it will ignore it. Again, stupid syntax.
ubuntu@web1:~$ sudo ls /root >>> /etc/sudoers: syntax error near line 31 <<< sudo: parse error in /etc/sudoers near line 31 sudo: no valid sudoers sources found, quitting sudo: unable to initialize policy plugin
Your /etc/sudoers file probably looks something like this:
# User privilege specification root ALL=(ALL:ALL) ALL # Members of the admin group may gain root privileges %admin ALL=(ALL) NOPASSWD:ALL # Allow members of group sudo to execute any command %sudo ALL=(ALL:ALL) ALL # See sudoers(5) for more information on "#include" directives: includedir /etc/sudoers.d
NOPASSWD does not work
If you set the NOPASSWD option for a user or group in sudo and it does not seem to work then you most likely have the order of statements wrong. The last statement in a sudoers file wins. Don't forget the files imported from /etc/sudoers.d. For example, the following will not work if noah is also a member of the sudo group because the sudo group definition comes after and overrides the NOPASSWD option.
noah ALL=(ALL) NOPASSWD:ALL # Allow members of group sudo to execute any command %sudo ALL=(ALL:ALL) ALL
The fix is to define the noah user options after the sudo group.
# Allow members of group sudo to execute any command %sudo ALL=(ALL:ALL) ALL noah ALL=(ALL) NOPASSWD:ALL
Set timestamp timeout
The following sets the timestamp timeout to 30 minutes for the given username, noah.
Defaults:noah timestamp_timeout=30
The following sets the timestamp timeout to 30 minutes for all users:
Defaults timestamp_timeout=30
Remove timestamp
Sometimes for scripting you want sudo authentication to be consistent. If sudo is going to ask for a password then it is preferable to have it ask every time rather than ask once and then not again unless a timeout is reached in which case it will ask again. This can be difficult to script for. It's easier just to expect the password every time. You can pass sudo an option, -k to clear the timestamp. Note that there is a similar -K option (capital K) which must be use alone without a command to be run. Also note that the NOPASSWD option will still override the -k option.
sudo -k id
No password
Allow a specific user, noah to sudo without a password:
noah ALL=(ALL) NOPASSWD:ALL
Allow all users in the admin group to sudo without a password:
%admin ALL=(ALL) NOPASSWD:ALL