06.linux basic-operations-2

Linux: Basic Operations - 2

Minsuk Lee
Hansung University, Seoul, Korea
minsuk@hansung.ac.kr

NEAOSS MC2.0 CC-BY 2.0 KR, © Korea OSS Promotion Forum, NIPA

Simple Shell usage
• Invoking Terminal 

• Type any command and [ENTER]
• BIG TIPs !!
– Use ‘←,↑→↓’, [INS], [DEL],[HOME],[END] keys to edit command line
– Try [tab] - It completes filename or shows all available choices
– When output stops, try [SPACE], mouse scroll, ‘q’ to continue or to quit
– $ exit -- will end the terminal


man (1)
• Shows manual page of Linux commands, libraries, utilities
• Usage : $ man [options] [section] item
– Item can be program, function, file, anything in /usr/share/man/*/
• Options :
– Sections
1. Executable programs or shell commands
2. System calls (functions provided by the kernel)
3. Library calls (functions within program libraries)
4. Special files (usually found in /dev)
5. File formats and conventions e.g. /etc/passwd
6. Games
7. Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7)
8. System administration commands (usually only for root)
9. Kernel routines [Non standard]

‘$ man printf ‘ show man page of shell command printf
‘$ man 3 printf ‘ show man page of printf() library
‘$ man -a printf ‘ show man page of both of the two


man (2)
• Options :
-a : display all available manual pages of the item
-k : list all man page items includes the given item name ($ apropos –r item)
-f : shows very short descriptions
-Tps : output as Postscript format (to be converted into pdf)

• Example
$ man man
$ man -Tps 3 printf | ps2pdf - printf.pdf

• Alternatives
$ info item : shows detail information, if the item is available in /usr/share/info
$ command –help : shows help messages (options) of the command

• PLEASE READ MAN PAGES OF COMMANDS, FUNCTIONS YOU USE !!


Name pattern matching
• Specifying multiple files(directories)
– Work for ALL commands
• ‘*’ means any string (multiple, any characters including null)
• ‘?’ means any single character
• [a-s] : means any single character between ‘a ’ and ‘s ’
– E.g., [1-7c-f], [acf2A-Z], …

– ‘$ rm * ’ : means everything in current directory
– ‘$ rm directory/* ‘ : means everything in directory
– ‘$ rm s*s ‘ : means files or directories start and end with ‘s ’
– ‘$ rm 6[ab]x* ‘ : means files or directories start with ‘6ax ’ or ‘6bx ’

• See man page of bash ( $ man bash ) for more
– Such as ?(patten-list), *(patten-list), +(pattern-list), …


Pipe and redirection
• Standard Input and Output
– In Shell, It’s Keyboard input and Screen Output, by default
– Pipe feeds standard output into other command’s standard input
– Redirection redirects the standard input/output from/to files

‘$ ls –l | more’ : feed the output of ‘ls –l’ to ‘more’
‘$ ls –1 | sort –r | more’ : ‘ls -1’ then, ‘sort’ in reverse order, and ‘more’
‘$ ls –l > file ’ : redirect the output of ‘ls –l’ to file (overwrite or create)
‘$ ls –l >> file ’ : redirect the output of ‘ls –l’ to file (append)
‘$ cat a b > c ’ : concatenate file ‘a ‘ and ‘b ‘ into file ‘c ‘
‘$ sort < source > destination ’ : ‘sort’ source, into destination

• Standard Error
‘$ command 2> file’ : redirect error message of command to file


grep
• Prints lines matching a pattern
• Usage : $ grep [options] pattern file…
• Options :
– -i : ignore case
– -n : print line number
– -H : with file name
– -r : read all files under directory recursively


find (1)
• Searches for files in a directory hierarchy
• Usage : $ find [options] [path...] [expression]
• Options :
-H, -L, -P : controls symbolic links (see, $man find)
• Expression for [match test] [Action] :
– Match test
-name : ‘$ find / -name thisname’ finds files with thisname, thisname can be pattern (*, ?, …)
-executable : executable files
-user : ‘$ find / -name user1’ finds files belonging to user1
-atime : ‘$ find / -atime n’ finds files accessed within n days
-ctime , -mtime : files created or modified within n days
-newer : ‘$ find / -newer file’ finds files modified more recently than file
-type c : ‘$ find / -type c’ finds files of type c, (c can be ‘d’ : directory, ‘f’ : regular file, ‘l’ : symbolic link, ‘b’,’c’:
device file)
-…
– Action
-delete : delete the found files
-exec command : apply command to the found files
in command ‘{}’ is used for found file
command ends with ; ( is escape code)
-…

find (2)
• Example
– Just find

– find and grep


ps
• Reports a snapshot of the current processes
• Usage : ps [options]
• Options :
ax : all process in system, same as ‘–e’
r : only running process
nnn : only process id nnn, same as ‘-pid pid_list list’ (e.g., ‘$ ps –pid 107,109’)
l, s, u, v, x : format long, signal, user-oriented, virtual memory, register format
m : shows threads after process


pstree
• Display a tree of processes
• Usages : $ pstree [options] [pid_or_user]
– $ pstree myuser (Terminal related part)
– $ pstree


top (1)
• Display Linux tasks
• Usage : $ top [options] [pid…]

[Commands to change ]

See man page !

top (2)
‘;’ multiple commands
‘>’ redirection

<type x.c>
<endless loop code>
x.c
Ctrl-D to end edit
Compile x.c to loop
‘&’ execute background

execute ./loop

Ctrl-Z to suspend

‘bg’ resume in background


top (3)
• top with a endless loop task

• top with two endless loop tasks


kill
• Send a signal to a process
• Usage : $ kill –signal [pid]
– $ kill -9 100 : kills process 100
– $ kill -9 -1 : kill all (you can kill)
• Signals :
-9 (KILL) : kill process
-1 (HUB) : restart
Others : see man page !


tar, bzip2, gzip (1)
• Compresses files and directories
• Usage : $ tar [options] path…
– $ tar cvf name.tar directory : Archive (no compress) directory into name.tar
– $ tar xvf name.tar : Extract name.tar
• Options :
– c : create, x : extrace, t : list
– v : verbose (lists file names)
– j : use bzip2, z : use gzip for compress / uncompress
– f filename : specify archive filename
• Bzip2 : compress a file into file.bz2
– ‘$ bzip2 file ’ to compress, ‘$ bzip2 –d file.bz2 ’ to uncompress
• gzip : compress a file into file.gz
– ‘$ gzip file ’ to compress, ‘$ gzip –d file.gz ’ to uncompress

• Example
– ‘$ tar cjf file.bz2 files-directories ‘ : tar & compress files-directories into file.bz2
– ‘$ tar xjvf file.bz2 ‘ : uncompress and untar file.bz2

tar, bzip2, gzip (2)

tar & bzip2

list archive

Remove temp directory

un-bzip2 and untar


df, du
• df report file system disk space usage
• Usage : $ df [options] [file]
• Options
-h : human readable units !

• du estimates file space usage
• Usage : $ du [options] [file]
• Options
-h : human readable units !
-s : display only total


sudo
• Execute a command as another user (such as super user)
• Usage : $ sudo [–u username] [command]
– $ sudo –u other-user /bin/bash : invoke shell with user other-user
– $ sudo /bin/bash : invoke superuser’s shell
– $ sudo command : run command in superuser permission

• Only selected user can get superuser permission
• (defined in /etc/sudoers)

?
$ sudo rm -rf ./*
vs.
$ sudo rm –rf /*

chown, chmod
• Changes owner, permission of files and direct
• Usage : $ chown [owner][:group] file…
$ chmod mode file…
• Options
-R : recursively change
• Permission issue
– $ chown can be done by superuser
– $ chmod needs enough permission

• Permission (read,write,execute)

mRWXRWXRWX
user others
group

Type (file, directory, device)


hostname, uname
– $ hostname : name of this computer
• Search domain, name server are defined in /etc/resolv.conf
– $ uname : Operating System Name as compiled


ifconfig
Use GUI
• Configures a network interface
To configure Network !
• Usage : $ ifconfig [interface or –a]
$ ifconfig interface [aftype] options | address ...
– interface is the name of network device
• (e.g., eth0 : Ethernet, lo : loopback)


ping
• Send ICMP ECHO_REQUEST to network hosts
• Usage : $ ping [options] destination
– destination is ip-address (a.b.c.d) or hostname
• Options :
-c count : stop after count
-i interval : ping interval
-n : display ip address rather than hostname
-s packetsize : set packet size


netstat (1)
• Prints network connections, routing tables, interface statistics,
masquerade connections, and multicast memberships
• Usage : $ netstat [options]
• Options :
-r : print routing table
-i : print interface statistics
-n : display ip address rather than hostname
-p : print pid and program name
-l : print only listening sockets
-a : print both listening & non listening
-t, -u : print socket using tcp, udp protocol


netstat (2)


Network files
• /etc/hosts : stores hostname and ip-address

• /etc/resolv.conf : ip-address of name server
• /etc/services : name of network services


Let’s Practice
• find & grep
– Build up directories
– Try $ find , $ grep, and mix it
• Top
– Edit ‘x.c’, compile into ‘loop’
– $ top
– Run ‘loop’ background and $ top,
– And once more, see how ‘loop’ processes share the CPU
– Try ‘$ pstree’ to find ‘loop’ process
– $ kill the ‘loop’ process
• Tar, bzip2
– As in slide
• Try $ df, $ du, $ chown, $ chmod, $ sudo
• Try $ ping, $ netstat [options], $ ifconfig


06.linux basic-operations-2

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