Introduction to System Admin

1. Introduction to System Admin Sirak Kaewjamnong

2. The system administration’s job • Adding a new user • Doing backup and restoring files from backups • Answer user questions • Monitoring system activity and tuning system performance for good respond time • Worrying about system security and patching security holds

3. The system administration’s job • Installing programs and OS updates • Trying to free up disk space • Rebooting the system after a crash • Adding a new equipment and new systems • Fixing any problems • Writing scripts to automate as many of the above activities as possible

4. Unix superuser • Superuser is a privileged account with unrestricted access to all files and command • The user name of superuser is “root” • This user has a user ID of 0

5. Becoming root • There are two ways to become the superuser • Login as root directly • Execute command su to change privileged • % su

6. Sudo command • The sudo utility allows users defined in the /etc/sudoers configuration file to have temporary access to run commands they would not normally be able to due to file permission restrictions • Sudo (superuser do) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root

7. The /etc/sudoers File • The /etc/sudoers file contains all the configuration and permission parameters needed for sudo to work

8. Format of the /etc/sudoers File usernames/group servername = (usernames command can be run as) command • Groups are the same as user groups and are differentiated from regular users by a % at the beginning. The Linux user group "users" would be represented by %users. • can have multiple usernames per line separated by commas. • Multiple commands also can be separated by commas. Spaces are considered part of the command. • The keyword ALL can mean all usernames, groups, commands and servers. • If run out of space on a line, admin can end it with a back slash (\) and continue on the next line. • The NOPASSWD keyword provides access without prompting for your password.

9. /etc/sudoers Examples root ALL = (ALL) ALL %wheel ALL = (ALL) ALL • root and users in group wheel can run anything on any machine as any user Srk,rp ALL = NOPASSWD: ALL • User srk and rp can run anything on any machine without a password peter, %operator ALL= /sbin/, /usr/sbin, /usr/local/apps/check.pl • user peter and all the members of the group operator to gain access to all the program files in the /sbin and /usr/sbin directories, plus the privilege of running the command /usr/local/apps/check.pl

10. Using Aliases in the sudoers File User_Alias ADMINS = millert, mikef, dowdy ADMINS ALL = NOPASSWD: ALL • User aliasADMINS are user millert.mikef,dowdy • User aliasADMINS can run anything on any machine without a password Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown srk ALL = PRINTING, /usr/bin/adduser • User srk can use printer and add new user

11. How to add user • Add linux group #groupadd students #groupadd staff #groupadd teachers • Add the Linux users and assign them to their respective groups #useradd –g teachers rp #useradd –g staff srk • Each user's personal directory is placed in the /home directory. The directory name will be the same as their user name

12. Change password • User root changing the password for user paul [root@myhost]# passwd paul Changing password for user paul. New password: Retype new password: passwd: all authentication tokens updated successfully. [root@myhost]#

13. Delete user • The userdel command is used to remove the user's record from the /etc/passwd and /etc/shadow used in the login process. The command has a single argument, the username [root@myhost]# userdel paul • an optional -r switch that additionally removes all the contents of the user's home directory [root@myhost]# userdel -r paul

14. http://www.sudo.ws/sudo/sample.sudoers