UNIX 1 1 UCF Course Content 2008 Wipro

UNIX 1. 1 UCF - Course Content © 2008 Wipro Ltd - Confidential

UNIX Operating System © 2008 Wipro Ltd - Confidential

Operating System (OS) • OS is a system software • OS provides an environment for execution of programs • OS acts as an interface between the user and the hardware of the computer system. • Kernel is the Core of the OS • Unix kernel program is a combination of 2 programs genunix (generic unix) and unix. © 2008 Wipro Ltd - Confidential

Features of UNIX • • • Multi-user, multitasking, timesharing Portability Modularity File structure Security © 2008 Wipro Ltd - Confidential

Layered Architecture KERNEL HARDWARE SHELL © 2008 Wipro Ltd - Confidential

Unix File System - Directories Directory Description / Primary hierarchy root and root directory of the entire file system hierarchy. /bin/ Essential command binaries that need to be available in single user mode ; for all users, e. g. , cat, ls, cp. /etc/ Host-specific system-wide configuration files /home/ Users‘ home directories , containing saved files, personal settings, etc. ; normally a separate partition. /opt/ Optional application software packages. /sbin/ Essential system binaries, e. g. , init, ip, mount. /tmp/ Temporary files /usr/ Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications. © 2008 Wipro Ltd - Confidential

UNIX Commands © 2008 Wipro Ltd - Confidential

Login and authentication login access computer; start interactive session logout disconnect terminal session passwd change local login password; you must set a strong password that is not easily guessed sudo allows users to run programs with the security privileges of another user (normally the superuser, or root) © 2008 Wipro Ltd - Confidential

Information date show date and time history list of previously executed commands man show online documentation by program name who is on the system and what they are doing whoami who is logged onto this terminal top show system stats and top CPU using processes uptime show one line summary of system status © 2008 Wipro Ltd - Confidential

File management cat combine files cp copy files ls list files in a directory and their attributes mv change file name or directory location rm remove files ln create another link (name) to a file chmod set file permissions chown Change ownership of file/directory gzip, gunzip compress/decompress a file find files that match specific criteria © 2008 Wipro Ltd - Confidential

Display contents of files cat copy files to display device more show text file on display terminal with paging control head show first few lines of a file(s) tail show last few lines of a file; or reverse line order vi full-featured screen editor for modifying text files grep display lines that match a pattern diff compare two files and show differences file examine file(s) and guess type: text, data, program, etc. wc count characters, words, and lines in a file © 2008 Wipro Ltd - Confidential

Directories cd change to new directory mkdir create new directory rmdir remove empty directory (you must remove files first) mv change name of directory pwd show current directory © 2008 Wipro Ltd - Confidential

Disks df summarize free space on disk filesystems du show disk space used by files or directories © 2008 Wipro Ltd - Confidential

Special character handling * match any characters in a file name ~user shorthand for home directory of user $name substitute value of variable name turn off special meaning of character that follows ' in pairs, quote string with special chars, except ! " in pairs, quote string with special chars, except !, $ ` in pairs, substitute output from enclosed command © 2008 Wipro Ltd - Confidential

Controlling program execution & run job in background ^c kill job in foreground ^z suspend job in foreground fg restart suspended job in foreground bg run suspended job in background ; delimit commands on same line ps show process information kill background job or previous process © 2008 Wipro Ltd - Confidential

Controlling program input/output tee copy input to both file and next program in pipe script make file record of all terminal activity Printing (BSD based) lpr send file to print queue lpq examine status of files in print queue lprm remove a file from print queue © 2008 Wipro Ltd - Confidential

Networking/communications ssh remote login/command execution; encrypted scp remote non-interactive file copy; encrypted sftp remote interactive file copy; encrypted telnet remote network login; plain text password - not recommended ftp network file transfer program; plain text password - not recommended © 2008 Wipro Ltd - Confidential

VI Editor • Two modes of the vi editor – Command mode: Can perform commands in the vi editor(default mode) – Editing (Insert) mode: Can type information in the vi editor • Why learn the vi editor? – The vi editor is the most frequently used editor in all flavors of Linux and UNIX – It is also useful in case the flavor of Linux/UNIX does not have a graphical interface © 2008 Wipro Ltd - Confidential

Some Simple VI Commands j move cursor down one line k move cursor up one line h move cursor left one character l move cursor right one character u UNDO WHATEVER YOU JUST DID; a simple toggle i insert text before cursor, until <Esc> hit a append text after cursor, until <Esc> hit o open and put text in a new line below current line, until <Esc> hit O open and put text in a new line above current line, until <Esc> h : q Quit a file ( use : q! forceful quit without saving) : w Save a file © 2008 Wipro Ltd - Confidential

File Access Permissions • Refers to the permissions associated with a file with respect to the following • Permission Levels • User (owner) (u) • Group (wheel, staff, daemon, etc. ) (g) • World (guest, anonymous and all other users) (o) • Permission Settings • Read (r) • Write (w) • Execute (x) © 2008 Wipro Ltd - Confidential

Changing Permissions - chmod • chmod u+x file_name Syntax: chmod <category> <operation> <permission> <filename(s)> or chmod <octal number> filename Octal Number 4 - for read 2 - for write 1 - for execution $ chmod 744 xyz this sets read, © 2008 write and execute permissions for Wipro Ltd - Confidential

Directory Creation/Removal Command Syntax mkdir [OPTION] DIRECTORY rmdir [OPTION] DIRECTORY $ mkdir(rmdir) <path>/<directory> $ mkdir(rmdir) –p <directory 1>/<directory 2>/<directory 3> Example: $ mkdir project 1 This creates a directory project 1 under current directory $ mkdir –p project 2/project 1 This creates 2 level of directories $rmdir –p dir 1/dir 2/dir 3 Remove the directory recursively © 2008 Wipro Ltd - Confidential

Command - cd cd command is used to change the directory • cd - take to the home directory • cd. . - takes to the parent directory • cd / - takes to the root directory • cd ~user - takes to the user home directory. © 2008 Wipro Ltd - Confidential

File-Related Commands File Operation Command Copying a file cp Moving a file mv Removing a file rm Displaying a file and concatenating files cat Command - cp Used to copy files across directories Syntax cp <source file> <new file name> Example cp file 1 file 2 © 2008 Wipro Ltd - Confidential

Command - cp Options to cp • -p • Copies the file and preserves the following attributes • • owner id group id permissions last modification time -r • recursive copy; copy subdirectories under the directory if any -i • interactive; prompts for confirmation before overwriting the target file, if it already exists © 2008 Wipro Ltd - Confidential

Command - mv Used to move a file, or rename a file Preserves the following details • owner id • group id • permissions • Last modification time -f suppresses all prompting (forces overwriting of target) © 2008 Wipro Ltd - Confidential

Command - rm Used to remove a file • Syntax : rm file(s) -f suppresses all prompting -i prompts before deleting destination file -r will recursively remove the file from a directory (can be used to delete a directory along with the content ) Caution: Use “i” option along with “r” to get notified on deletion © 2008 Wipro Ltd - Confidential

Command – chown & chgrp $ ls –l -rwxr-xr-x 1 user 1 training 3 user 1 faculty 12373 Dec 15 14: 45 a. out 4096 Dec 24 11: 56 awkpro $chown user 2 a. out $ls –l -rwxr-xr-x 1 user 2 training 3 user 1 faculty 12373 Dec 15 14: 45 a. out 4096 Dec 24 11: 56 awkpro $ chgrp training awkpro $ls –l -rwxr-xr-x 1 user 2 training 3 user 1 training 12373 Dec 15 14: 45 a. out 4096 Dec 24 11: 56 awkpro © 2008 Wipro Ltd - Confidential

Command - ln Linking files • Hard Link (in the same filesystem) • $ ln /usr/bin/clear /usr/bin/cls • Hard link uses the same inode number • Soft Link (in different filesystems also used to link directories) • $ ln –s /usr/bin/clear /home/user 1/cls © 2008 Wipro Ltd - Confidential

Standard Files • Standard Input file • Keyboard, file descriptor is 0 • Standard Output file • Monitor, file descriptor is 1 • Standard Error file • Monitor, file descriptor is 2 © 2008 Wipro Ltd - Confidential

I/O Redirection < file redirect standard input from file > file redirect standard output to file 2> file redirect standard error to file 2>&1 merge standard error with standard output $ cat > abc $ ls –l > outfile $ cat xyz abc > outfile 2> errfile $ cat xyz abc > outfile 2>&1 © 2008 Wipro Ltd - Confidential

Filters • Filters are programs that takes its input from the standard input file, process it, and sends it to the standard output file. • Commonly used filter commands • sort • grep • cut • head • tail • paste © 2008 Wipro Ltd - Confidential

sort Sorts the contents of the given file based on the first char of each line. -n numeric sort (comparison made according to strings numeric value) -r reverse sort Example: $ du /home | sort –nr list files from /home in decreasing order of their file size grep (global regular expression print) • grep -Global Regular Expression Printer is used for searching regular expressions • Syntax • grep <options> <pattern> <filename(s)> © 2008 Wipro Ltd - Confidential

grep options -c -n -v -i displays count of line where the pattern occurs displays line numbers along with the lines displays all lines except lines matching pattern Ignores case for matching Patterns: * matches 0 or more characters ^pqr Matches pqr at the beginning of the line pqr$ Matches pqr at the end of the line “. ” Matches any one character © 2008 Wipro Ltd - Confidential

Filter Command – head / tail head: Displays the first n lines of the file $ head -3 file 1 tail: Displays the last n lines of a file $ tail -3 file 1 Can also specify the line number from which the data has to be displayed till the end of file $ tail +5 file 1 © 2008 Wipro Ltd - Confidential

Command Piping • Allows the output (only the standard output) of a command to be sent as input to another command. • Multiple pipes may appear in one command line. Example: $ cat file 1 | head | wc -l © 2008 Wipro Ltd - Confidential

ftp - commands • File Transfer Protocol (FTP), a standard Internet protocol, is the simplest way to exchange files between computers • FTP service runs on Port 21 • Ftp program supports the following commands § get receive file from host § mget receive multiple files from host § put send file to host § mput send multiple files from host © 2008 Wipro Ltd - Confidential

ftp - commands Ftp program supports the following commands as well § ls list directory of host § cd change directory on the host § lcd change directory on the local machine To set transfer format § asc / ascii § bin/ binary set to ascii mode set to binary mode Progress indication of transfer (to see the data flow) § hash command Quitting ftp session § bye command © 2008 Wipro Ltd - Confidential

Tape Archive - tar • Tar is an archiving utility to store and retrieve files from an archive, known as tar file. • Archives and extracts files to and from a single file called a tar file. • Though archives are created on a tape, it is common to have them as disk files as well. • SYNTAX tar c|t|x [vf destination] source. . . c – create a tar file t – list the contents of the tar file x – extract the contents of the tar file. © 2008 Wipro Ltd - Confidential

Tape Archive - tar Examples: • $ tar –cvf my. tar *. dat Create a new tar file containing all. dat files (assuming a. dat, b. dat and c. dat exist) • $ tar –xvf my. tar Extract the contents of the tar file my. tar • $tar -c file 1 file 2 write the file 1 and file 2 files to a new archive on the default tape drive • $tar -xf my. tar test. file Extract test. file from the tar file my. tar • $tar –tvf my. tar view the contents of the tar file called my. tar © 2008 Wipro Ltd - Confidential

find • Lets user to search set of files and directories based on various criteria Syntax: find [path. . . ] [expression] [path] where to search [expression] • What type of file to search (specified with –type option) • What action to be applied (–exec, –print, etc. ) • Name of the files (specified as part of –name option, enclosed in “ “) Examples • $ find. –name “*. c” -print lists all files with. c extension from the current dir & its subdirectories • $ find /etc -name hosts Will find the file named “hosts” under /etc and print --- /etc/hosts © 2008 Wipro Ltd - Confidential

find • $ find /home lists all files and directories under /home • $ find. –atime 2 lists files accessed exactly 2 days ago • $ find. –atime +2 lists files accessed more than 2 days ago • $ find / –mtime – 2 lists files modified less than 2 days ago © 2008 Wipro Ltd - Confidential

Sed • Sed is a stream editor. A stream editor is used to perform basic text transformations on an input stream (a file or input from a pipeline). • But it is sed's ability to filter text in a pipeline which particularly distinguishes it from other types of editors. Ø Example 1: command to change a to A and b to B in a file called ‘test’ is - #sed -e 's/a/A/' -e 's/b/B/' test Ø Example 2: find and replace the word “star" to “planet" globally in the file called ‘universe’ is - #sed '/s/star/planet/g' universe © 2008 Wipro Ltd - Confidential

IOSTAT / NETSTAT / VMSTAT • The iostat utility displays kernel I/O statistics on terminal, device and cpu operations. Example : Display tty statistics every 10 seconds – $ iostat –t 10 • netstat - Display network connections, routing tables, interface statistics, masquerade connections, and multicast memberships Example : command to display the Interface statistics - $ netstat –i and command to display routing table - $ netstat –nr • vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity. Example : To display five summaries at 2 -second intervals - $ vmstat 2 5 © 2008 Wipro Ltd - Confidential

Job Scheduling • ‘at’ : In Unix the at command is used to schedule other to be executed once, at a particular time. More precisely, it reads a series of commands from standard input and collects them into one "at-job" which is carried out at a later date. Ø Example : $ echo "cc -o test. c" | at 1145 $ at 1145 jan 31 at> cc -o test. c at> ^D ‘Cron’ : is a time-based job scheduer in Unix. Cron enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates. It is commonly used to automate system maintenance or administration. Ø Example : command t list all cronjobs - $ crontab –l, command to execute a cron job $ crontab –e <job name> and command to remove a cron job - $ crontab –r <job name > © 2008 Wipro Ltd - Confidential

Unix Process and PS • • • Process - a program in execution When program is executed, a new process is created The process is alive till the execution of the program is complete Each process is identified by a number called pid The ps command is used to display the characteristics of a process It fetches the pid, tty, time, and the command which has started the process. Ø -f lists the pid of the parent process also. Ø -u lists the processes of a given user Ø -a lists the processes of all the users Ø -e lists all the processes including the system processes • Back Ground process : Ø Ø Enables the user to do more than one task at a time. If the command terminates with an ampersand (&), UNIX executes the command in the background Ø nohup – Lets processes to continue to run even after logout – The output of the command is sent to nohup. out if not redirected © 2008 Wipro Ltd - Confidential

Killing a Process, TOP and NICE • • kill: Kills or terminates a process kill command send a signal to the process Ø The default signal is 15 ( SIGTERM) kill -9 (SIGKILL) Ø Terminates the process abruptly pkill : command used to kill a process by name Ø pkill <command name> Ø Pkill -9 <ommand name> • ‘top’ Comamnd : Provides an ongoing look at processor activity in real time. It displays a listing of the most CPU-intensive tasks on the system, and can provide an interactive interface for manipulating processes. • ‘nice’ Command : The nice command lets you run a command at a priority lower than the command's normal priority. If you do not specify an Increment value the nice command defaults to an increment of 10. The priority of a process is often called its nice value. © 2008 Wipro Ltd - Confidential

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