UNIX/LINUX OPERATING SYSTEM

1. UNIX/LINUX OPERATING SYSTEM

2. Linux Commands UNIX/LINUX Commands • A command is a program which interacts with the kernel to provide the environment and perform the functions called for by the user. • A command can be: a built-in shell command; an executable shell file, known as a shell script; or a source compiled, object code file. • The shell is a command line interpreter. The user interacts with the kernel through the shell. You can write ASCII (text) scripts to be acted upon by a shell. • It reads the terminal input and translates the commands into actions taken by the system. The shell is analogous to command.com in DOS.

3. Linux Commands UNIX Shell • The original shell was the Bourne shell, sh. • Every Unix platform will either have the Bourne shell, or a Bourne compatible shell available. • The default prompt for the Bourne shell is $ (or #, for the root user). • Another popular shell is C Shell. The default prompt for the C shell is %.

4. Linux Commands Shell Programming • You can write shell programs by creating scripts containing a series of shell commands. • The first line of the script should start with #! which indicates to the kernel that the script is directly executable. • You immediately follow this with the name of the shell, or program (spaces are allowed), to execute, using the full path name. So to set up a Bourne shell script the first line would be: #! /bin/sh • The first line is followed by commands #!/bin/bash cd /tmp mkdir t • You also need to specify that the script is executable by setting the proper bits on the file with chmod, e.g.: $ chmod +x shell_script

5. Linux Commands LINUX COMMANDS • File Management and Viewing • Help, Job and Process Management • Network Management • System Management • User Management • Miscellaneous

6. Linux Commands Command Structure • Command <Options> <Arguments> • Multiple commands separated by ; can be executed one after the other

7. Linux Commands Help Facilities for Commands • To understand the working of the command and possible options use (man command) • Using the GNU Info System (info, info command) • Many tools have a long−style option, `−−help', that outputs usage information about the tool, including the options and arguments the tool takes. Ex: whoami --help

8. Linux Commands Pipes • An important early development in Unix was the invention of "pipes," a way to pass the output of one tool to the input of another. eg. $ who | wc −l By combining these two tools, giving the wc command the output of who, you can build a new command to list the number of users currently on the system

9. QUESTIONS?

10. Introduction to Linux Listing the Content of a Directory • ls is used to list the contents of a directory. • If the command ls is written with parameter –l then the command lists contents of the working directory with details. Example: $ ls –l

11. Introduction to Linux Moving in Directories • cd try_it Changes the directory to try_it • pwd Prints present working directory (e.g. /home/smith/try_it) • cd .. Move to superior directory pwd : Prints /home/smith • cd /home The absolute path pwd : Prints /home • cd The system is returned to the user home directory pwd : Print /home/smith

12. Introduction to Linux Make Directory • The command mkdir test makes new directory test (the path is given relative) as a subdirectory of the current directory.

13. Introduction to Linux Remove Directory • The command rmdir your_dir removes directory your_dir if it is empty. • The command rm –rf is used to delete a non empty directory

14. Introduction to Linux Copy File • The command cp file_1 file_2 copies file_1 to file_2. The both files must be in the same working directory. If they are in various directories, the path must be given.

15. Introduction to Linux Rename and/or Move the File • The command mv file_1 file_2 moves file_1 to file_2 • The both files must be in the same working directory. • If they are in different directories, the path must be given. • The file_1 is removed from the disk.

16. Introduction to Linux Remove File • The command rm file_a removes the file_a from the system • If you use wildcard. For example rm h*c you will remove all files beginning with h and ending with c which are in working directory. • If you write rm * you will erase all files from your working directory.

17. Introduction to Linux Access Permission of File/Directory • The ownership of the file or directory can be changed using the command chown <owner> <file/directory name> • The group of the file or directory can be changed using the command chgrp <group> <file/directory name> • The permissions of the file can be changed using chmod command chmod -R ### <filename or directory> • -R is optional and when used with directories will traverse all the sub-directories of the target directory changing ALL the permissions to ###.

18. Introduction to Linux Access Permission of File/Directory • The #'s can be: 0 = Nothing1 = Execute2 = Write3 = Execute & Write  (2 + 1)4 = Read5 = Execute & Read (4 + 1)6 = Read & Write (4 + 2)7 = Execute & Read & Write (4 + 2 + 1)

19. QUESTIONS?

20. Linux Commands Linux File Management and Viewing • find Find files (find <start directory> -name <file name> -print) Ex: find /home –name readme -print (Search for readme starting at home and output full path.)“/home" = Search starting at the home directory and proceed through all its subdirectories "-name readme" = Search for a file named readme "-print" = Output the full path to that file • locate File locating program that uses the slocate database. Ex: locate –u to create the database, locate <file/directory> to find file/directory

21. Linux Commands Linux File Management and Viewing File viewing and editing • vi Editor with a command mode and text mode. Starts in command mode. • gedit GUI Text Editor • tail Look at the last 10 lines of a file. Ex: tail -100 <filename> (looks at last 100 lines) • head Look at the first 10 lines of a file. (head <filename>)

22. Linux Commands Linux File Management and Viewing • cat View a file Ex: cat filename • grep List all files with the specified expression. (grep pattern <filename/directorypath>)Ex: ls –l |grep sidbi : List all lines with a sidbi in them. Ex: grep " R " : Search for R with a space on each side • sleep Delay for a specified amount of time. • sort Sort a file alphabetically. • uniq Remove duplicate lines from a sorted file. • wc Count characters, words and lines in a file. (wc –c/w/l <filename>).

23. Linux Commands Network Management Commands • ping Send ICMP ECHO_REQUEST packets to network hosts. (ping <remote-host-name/ip>) • ssh Secure Login (ssh <remote system name/ip>) • telnet User interface to the TELNET protocol, setting up a remote console session. (telnet <remote system name/ip>) • tcpdump Dump traffic on a network. Prints out headers of packets that match the boolean expression. (tcpdump eth0) • traceroute Print the route that packets take to the specified network host. (traceroute <remote system name/ip>)

24. Linux Commands System Management Commands • shutdown If your system has many users, use the command shutdown -h +time ‘<message>`, where time is the time in minutes until the system is halted, and message is a short explanation of why the system is shutting down. Ex: # shutdown -h +10 'We will install a new disk. System should be back on-line in three hours’. • passwd Set a user's pass word. (passwd, passwd <username>)

25. Linux Commands System Management Commands • su Single user login. (su -) • who Display the users logged in. • whoami Print effective user id.

26. Linux Commands Linux Job & Process Management Linux Process Management • ps Get the status of one or more processes. PPID-parent process ID ; PID-process ID Eg: ps ax |more to see all processes including daemons Eg : ps –ef | grep <process> • top The top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel

27. Linux Commands Linux Job & Process Management Linux Process Management • kill Ex: "kill 34" - Effect: Kill or stop the process with the process ID number 34. • killall Kill processes by name. • pid Find the process ID of a running program

28. QUESTIONS?

29. Linux System Administration SYS ADMIN TASKS • Setting the Run Level • System Services • User Management • Network Settings • Scheduling Jobs • Backup and Restore • Adding and Removing software/packages • Monitoring the system (general, logs)

30. Linux System Administration Init Runlevels • The following runlevels are defined in Linux: • 0 - halt (Do NOT set initdefault to this) • 1 - Single user mode • 2 - Multiuser, without Network (The same as 3, if • you do not have networking) • 3 – Text Mode • 4 - unused • 5 – Graphical Mode • 6 - reboot (Do NOT set initdefault to this)

31. Desktop Configuration Init Runlevels • The default runlevel for a system to boot to is configured in /etc/inittab. id:5:initdefault: • In GUI: Applications  System Settings  Server Settings Services • Generally, Linux operates in runlevel 3 or 5.

32. Linux System Administration Linux Services There are 113 deamons, each for a service or application. Some examples are: • httpd : Apache Web server • mysqld : MySQL server • named : DNS server • network : Networking • nfs : Network File Share • ntpd : NTP (Network Time Protocol) server

33. Linux System Administration Linux Services • Start/Stop boot time services in /etc/rc.d/rc3.d or /etc/rc.d/rc5.d • All services startup scripts which start with S will start at boot time and all startup scripts which start with K will not start at boot time. The number after S or K is the priority. K95kudzu K96pcmcia S56xinetd S60vsftpd • Use service <service name> start/stop/restart to start, stop or restart a service from command line

35. Linux System Administration Creating a new User Account • Add an entry in /etc/passwd and /etc/shadow file (use next uid and suitable gid). You will have to create the user directory and assign a password to the user • Use useradd or adduser command to create a new user (useradd –g <group> -d <home directory> -c <comment> -s <shell> login-name) and groupadd to create a new group (groupadd group-name). You will have to assign a password (passwd login-name) • In GUI: Applications  System Settings  Users and Groups

37. Linux System Administration /etc/passwd and /etc/shadow File • /etc/passwd Holds user account info Included fields are: • Login name • User Id (uid) • Group Id (gid) • General Comment about the user • Home Directory • Shell • /etc/shadow Contains the encrypted password information for users' accounts and optionally the password aging information.

38. Linux System Administration Removing a User Account • userdel –r <username> • Remove login id from /etc/passwd & /etc/shadow file and delete home directory • Use GUI to Delete the user

39. QUESTIONS?

40. Linux System Administration Linux Network Configuration • /etc/resolv.conf Tells the kernel which name server should be queried when a program asks to "resolve" an IP Address. nameserver 172.31.1.1 search cc.iitk.ac.in iitk.ac.in • /etc/sysconfig/network Indicates networking is enabled (NETWORKING=yes) and provides information on hostname, gateway and nis domain. NETWORKING=yes HOSTNAME=webhome.cc.iitk.ac.in GATEWAY=172.31.1.250

41. Linux System Administration Linux Network Configuration • /etc/sysconfig/network-scripts/ifcfg-eth0 Network configurations like boot protocol (static/dhcp), ip address, netmask, network address, broadcast address etc. DEVICE=eth0 ONBOOT=yes BOOTPROTO=static IPADDR=172.31.1.40 NETMASK=255.255.0.0 BROADCAST=172.31.255.255 NETWORK=172.31.0.0 GATEWAY=172.31.1.250

43. Linux System Administration Scheduling Jobs: Cron • Cron is a program that enables you to execute a command, or a script with a sequence of commands, at a specified date, time or at set intervals. • Add the job script in /etc/cron.hourly or /etc/cron.daily or /etc/cron.weekly or /etc/cron.monthly to schedule a job

44. Linux System Administration Backup & Restore • Backup the user area or configuration file • Use tar to take backup on a different disk or tape • Backup can be scheduled using cron • Backup: tar –zcvf <tar filename> <Directory Tree to be backedup> • Restore: tar –zxvf <tar filename> <file to be recovered> • Backup should be occasionally checked by restoring it • Backup Policy: Full Backup every weekly/fortnightly and incremental backup every day

45. Linux System Administration Adding & Removing Software • Download a binary • Download the source code and compile on the system (download, untar, configure, make, make install, make uninstall) • Use RPM - Redhat Package Manager and install rpms • www.rpmseek.com & www.rpmfind.net can be used to search and download rpms (i386 Binary RPMs or SRC RPMs) • For Binary rpms: rpm [options] rpm-file (rpm –qa, rpm –ivh, rpm –Uvh, rpm -e) Where -q= query, -a= all, -i=install, -v=verbrose, -U= upgrade, -h= hash, -e= erase • For Source rpms: rpmbuild –rebuild rpm-source-file Compiled binary rpms will be available at /usr/src/redhat/RPMS/i386 which can be installed

46. Linux System Administration Monitoring the System • Monitor Disk Usage (df) • Monitor CPU and Memory utilization (top) • Monitor process/services (ps, pgrep) • Monitor logs (/var/log/messages) • GUI Tool (Applications System Tools System Performance)

47. QUESTIONS?