====== RH124 sudo and sudoers file ======

===== Ask Google =====

Does EX200 exam ask about sudo and sudoers file?

//"Yes, the Red Hat Certified System Administrator (RHCSA) EX200 exam can test you on sudo and the sudoers file as part of its User and Group Management objectives."//

===== Links =====

  * [[https://www.sudo.ws/|sudo home page]]
  * [[www.geeksforgeeks.org/linux-unix/sudo-command-in-linux-with-examples/|sudo Command in Linux]]
  * [[https://www.digitalocean.com/community/tutorials/how-to-edit-the-sudoers-file|How to edit the sudoers file]]
===== The "wheel" group =====

All members of the ''wheel'' group can run the ''sudo'' comamand, but will still have to enter their personal password by default.

===== Using the same sudoers file across multiple hosts =====

You can use the same ''/etc/sudoers'' file or synchronized rules across multiple Linux servers, should you want to standardize administrative access; this is done by using the ''Host_Alias'' directive to define specific groups of machines and assign rules to them. 

===== General format of sudoers line =====

<code>
username hostname = (run_as_user:run_as_group) tag:command
</code>

Examples:

<code>
username ALL=(ALL:ALL) ALL
username ALL=(ALL) ALL         (shorter form of above)
%groupname ALL=(ALL) NOPASSWD: ALL
%groupname ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart nginx
%groupname host1,host2,host3=(ALL) ALL
username host_alias=(ALL) ALL
</code>

===== Very abbreviated /etc/sudoers =====

Note much of this file is commented out.

<code>
## This file must be edited with the 'visudo' command.

## Host Aliases
## Groups of machines. You may prefer to use hostnames (perhaps using 
## wildcards for entire domains) or IP addresses instead.
# Host_Alias     FILESERVERS = fs1, fs2
# Host_Alias     MAILSERVERS = smtp, smtp2

## User Aliases
## These aren't often necessary, as you can use regular groups
## (ie, from files, LDAP, NIS, etc) in this file - just use %groupname 
## rather than USERALIAS
# User_Alias ADMINS = jsmith, mikem

## Command Aliases
## These are groups of related commands...

## Networking
# Cmnd_Alias NETWORKING = /sbin/route, /sbin/ifconfig, /bin/ping, /sbin/dhclient, /usr/bin/net, /sbin/iptables, /usr/bin/rfcomm, /usr/bin/wvdial, /sbin/iwconfig, /sbin/mii-tool

## Installation and management of software
# Cmnd_Alias SOFTWARE = /bin/rpm, /usr/bin/up2date, /usr/bin/yum

## Services
# Cmnd_Alias SERVICES = /sbin/service, /sbin/chkconfig, /usr/bin/systemctl start, /usr/bin/systemctl stop, /usr/bin/systemctl reload, /usr/bin/systemctl restart, /usr/bin/systemctl status, /usr/bin/systemctl enable, /usr/bin/systemctl disable

## Updating the locate database
# Cmnd_Alias LOCATE = /usr/bin/updatedb

## Storage
# Cmnd_Alias STORAGE = /sbin/fdisk, /sbin/sfdisk, /sbin/parted, /sbin/partprobe, /bin/mount, /bin/umount

## Delegating permissions
# Cmnd_Alias DELEGATING = /usr/sbin/visudo, /bin/chown, /bin/chmod, /bin/chgrp 

## Processes
# Cmnd_Alias PROCESSES = /bin/nice, /bin/kill, /usr/bin/kill, /usr/bin/killall

## Drivers
# Cmnd_Alias DRIVERS = /sbin/modprobe

... big snip ...

## Next comes the main part: which users can run what software on 
## which machines (the sudoers file can be shared between multiple
## systems).
## Syntax:
##
## 	user	MACHINE=COMMANDS
##
## The COMMANDS section may have other options added to it.
##
## Allow root to run any commands anywhere 
root	ALL=(ALL) 	ALL

## Allows members of the 'sys' group to run networking, software, 
## service management apps and more.
# %sys ALL = NETWORKING, SOFTWARE, SERVICES, STORAGE, DELEGATING, PROCESSES, LOCATE, DRIVERS

## Allows people in group wheel to run all commands
%wheel	ALL=(ALL)	ALL

## Same thing without a password
# %wheel	ALL=(ALL)	NOPASSWD: ALL

## Allows members of the users group to mount and unmount the 
## cdrom as root
# %users  ALL=/sbin/mount /mnt/cdrom, /sbin/umount /mnt/cdrom

## Allows members of the users group to shutdown this system
# %users  localhost=/sbin/shutdown -h now

## Read drop-in files from /etc/sudoers.d (the # here does not mean a comment)
#includedir /etc/sudoers.d
</code>

Note well the final ''#includedir'' directive, which further processes sudo files from that directory in alphabetical order.

===== Giving the class sudo access =====

==== Option 1 ====

Add all class accounts to the ''wheel'' group; you still might need to type your password.

==== Option 2 ====

Create a new group, ''class'', add all students to that ''class'' group, and add a new file under ''/etc/sudoers.d'' with **either** of these two lines:

<code>
%class ALL=(ALL) ALL
%class ALL=(ALL) NOPASSWD: ALL
</code>

===== How to examine your own sudo capabilities =====

<code>
$ sudo -l         (lower case "ell")
</code>