a quick introduction to linux

A Quick Introduction to A Quick Introduction to LinuxLinux(A compilation of some useful Linux commands)(A compilation of some useful Linux commands)

Tusharadri Sarkar

June 28, 2010

IBM

June 28, 2010 1Tusharadri Sarkar

A Brief History of UNIXA Brief History of UNIX

Bell Labs : 1970

The C programming language

Support for simultaneous users

Minimum effort for platform compatibility

Simple, elegant, and easy* to use

* Of course, we are talking about the CLI folks !!


A Brief History of LinuxA Brief History of Linux

The GNU project - Richard Stallman 1984

MINIX - Professor Andrew TanenbaumLinus Torvalds - inspired by MINIX

April 1991

Linux 0.01 releasedSeptember 1991


Linux Directory StructureLinux Directory Structure


Main DirectoriesMain Directories

/ The parent (root) directory

bin Compiled executable files (ls, grep)

boot Linux Kernel images and configs

etc System configuration files

dev Device files for all system H/Ws

home Stores home directories of users

lib System library files


Main DirectoriesMain Directories

usr Stores files and executables that all users can access

var Stores files whose size might vary

tmp Stores temporary files

sbinStores executables for system administrator, user can also access

procProvides Kernel windows to view system status (memory, IO etc.)


Users and GroupsUsers and Groups

Each “user” is a member of at least one “group” in Linux

Each user has a home directoryWhat are there in /home and /usr/users?UNIX permissions: both users and groups

> ls –l : see all permissions


Note: From now on, the > at the beginning of each command represents the command prompt. The command starts after that

Notes on File PermissionNotes on File Permission

In UNIX/Linux system everything is a fileFile has 3 permissions : read (r), write (w) and execute (x)

File has 3 sets of permissions: user – group – others

For each, permissions have weights: r = 4 w = 2 x = 1

So, what does permissions 755 means ?


Alias: To make life easy...Alias: To make life easy...

Pipes |: to chain multiple commandsAlias: Write commands once and execute them whenever you need

An example:> alias jtest=`find <JAVA_TEST_PATH> -name *.java |

grep 'Test' | sed 's/Test/TestCase/g'`

What does it do?The .bashrc file: Your own set of aliases


Directory NavigationDirectory Navigation


pwd Present Working Directory

cd Login (home) dir. of the user

cd – User’s last (previous) dir.

cd ~/<path> Here, ~ stands for ‘home’

cd /<path> Using absolute path

cd .. One dir. level up

'.' (dot) and '..' (dot dot) indicate current and parent directories, just like Windows

Creating & Removing DirectoriesCreating & Removing Directories

Check your permissions carefully:write permission – to create and remove

directories

Check your permissions again:not only user but group permissions

also matters

> mkdir <dname> : Create directory> rmdir <dname> : Remove directory


File Searching (ls)File Searching (ls)

ls: Stands for “List”> ls –a : Expose the hidden files> ls –lrt : Very useful when searching by last modification dates

Use regular expressions: ls –lrt lib*.soCreate alias of your own listing commands to make things easy for you again:

Example: > alias l=`ls –l --color=auto`


File Searching (find)File Searching (find)

find: A very powerful command for file searching operations

> find <path> -name *.txtTypical usage with regular expressions

> find <path> -type dwhen you are after the directories!!

> find <path> -type fwhen you are after the regular files!!


File Searching (find)File Searching (find)

find is more powerful when chained with other commands like xgrep or grep

For example:

> find <path> -name "*.*" -exec grep "<pattern>" '{}' \; -print 2>/dev/null

What does the above command do?


File Searching (grep)File Searching (grep)

grep: When you are interested in the contents of the files

Typical usage for search operations:

> grep '<pattern>' <files>When the pattern position also matters:

> grep –a N '<pattern>' <file>

> grep –b N '<pattern>' <file>

> grep –C N '<pattern>' <file>


File Searching (grep)File Searching (grep)

When you are looking for the line numbers: > grep –c '<pattern>' <file>

Remember: C and c are different options for 'grep'

The --color option: Highlight <pattern>Enhance power of 'grep' : 'find' and 'sed'Extremely useful if you are interested in Shell scripting


File Operations (Copy Move Delete)File Operations (Copy Move Delete)

cp – mv – rm: Straight forward and simpleThey have similar syntax and options:

> cp <source> <destination>

> mv <source> <destination>

> rm <filename>-i & -r : Do it 'interactively' or 'recursively'Be careful while using rm and move. Use > alias rm=`rm –i`; alias mv=`mv –i`


Archives and CompressionsArchives and Compressions

Need to create archive and compress files? It’s easy with tar and gzip:

> tar –cf demo.tar <file1> <file2> …> tar –xvf demo.tar - like verbose?

Zip and Unzip a file:gzip & gunzip :: bzip2 & bunzip2

Combine archiving and zipping together:> tar –czvf myfiles.tar.gz *.sh> tar –xzvf myfiles.tar.gz


Text Manipulation (sed)Text Manipulation (sed)

sed: Stands for “Stream Editor”

Powerful but also complexWhen it comes to text manipulation:

Combine powers of 'sed' and 'grep'General format of 'sed' for substitution:> sed 's/<pat1>/<pat2>/<switch>' file1 > file2

How does the <switch> influence the output?



9 typical ‘sed’ usage examples

Pattern substitutions:

1. > sed 's/string1/string2/g' – very basic

2. > sed 's/$.*$1/\12/g' – a little tricky !

3. > sed '/ *#/d; /^ *$/d' – trickier !!4. > sed ':a; /\\$/N; s/\\\n//; ta' – too cryptic !!!

What are all those '\' required for?



5. > sed 's/[ \t]*$//'

If you don't like spaces...6. > sed 's/$[`"$\]$/\\\1/g'

Use escape judiciously with meta-characters 7. > sed 10 | sed 's/^/ /; s/ *$.\{7,\}$/\1/'

Handy for number alignments8. > sed –n '1000{p;q}'9. > sed –n '10,20p;20q'

Printing with sed


Text Manipulation (tr)Text Manipulation (tr)

tr: Stands for “Translate”> echo 'Test' | tr '[:lower:]' '[:upper:]'

Case conversion> tr –dc '[:print:]' < /dev/urandom

Handle non printable characters> tr –s '[:blank:]' '\t' < /proc/diskstats | cut –f4

Combine with 'cut' to manipulate fields


Set Operations (sort)Set Operations (sort)

sort: is helpful with text filesuniq helps refining you sorting

> sort file1 file2 | uniq

> sort file1 file2 | uniq –d

> sort file1 file1 file2 | uniq –u

> sort file1 file2 | uniq –uWhat are the differences in output?


Set Operation (join)Set Operation (join)

join: works best on previously sorted files:

> join –t'\0' –a1 –a2 file1 file2

> join –t'\0' file1 file2

> join –t'\0' –v2 file1 file2

> join –t'\0' –v1 –v2 file1 file2On unsorted files join works just like concatenating files


Basic NetworkingBasic Networking

ifconfig: An equivalent of 'ipconfig' on DOS, but it does much more

> ifconfig

> ifconfig –< interface>

iwconfig: 'w' for wireless networkhostname: When you want to know about the host/ the system you are on

> hostname

> hostname –i June 28, 2010 25Tusharadri Sarkar

Basic NetworkingBasic Networking

netstat: Working with kernel routing table> netstat –r> netstat –i> netstat –l> netstat –tup

route: Modifying the kernel routing table> route add [route addr] [interface]> route delete [route addr] [interface]


Basic System InformationBasic System Information

> uname –aWhich OS, Kernel version, hardware and

system architecture am I running on? For specific information use the following:

-s, -o, -r, -v, -m, or -n

Know who all are working with you:> w> who> whoami

> who am i (Yes, the output is different!!) June 28, 2010 27Tusharadri Sarkar

Basic System InformationBasic System Information> head –n1 /etc/issue

What distribution version and release am I using?

> cat /proc/partitions

What about my partitions?> grep 'MemTotal' /proc/meminfo

Am I running out of RAM?> mount | column –t

What file systems is currently in use?June 28, 2010 28Tusharadri Sarkar

Disk Space UsageDisk Space Usage

> ls –lSr

'ls' command coming to rescue again!!du – Stands for “Disc Usage”

> du –s * | sort –k1,1rn | head

> du –hk .

> du –h <file>

df – Stands for “Disc Free”> df –h

> df –iJune 28, 2010 29Tusharadri Sarkar

Basic Monitoring & DebuggingBasic Monitoring & Debugging

If you want to monitor a file continuously:> tail –f <filename> You will need Ctrl+C too!!

When you want to deal with processes:> ps –ef <processname>

> ps –p pid1, pid2,... Be sure of PID & PPID !!

> ps –e –o pid, args --forest Hierarchical list

Some miscellaneous commands:> free –m> last reboot


Basic Monitoring & DebuggingBasic Monitoring & Debugging

3 Advance commands (for sysadmin)

Every CPU cycle is costly...> ps –e –o pcpu, cpu, nice, state, cputime,

args --sort pcpu | sed '/^ 0.0 /d'

And every byte of memory too...> ps –e –orss=, args= | sort –b –k1, 1n | pr –

TW$COLUMNS

Locked threads can cause troubles...> ps –C <process> -L –o pid, tid, pcpu, state


MiscellaneousMiscellaneous

Get familiar with the time keepers:

cal: “Calendar”, no one can live without it...

> cal (current month’s calendar)

> cal <mm> <yyyy> (for specific month)date: Of course you want to know this...

> date (Date with IST)

> date “%d/%m%y %H:%M:%S”

(A more familiar date format)June 28, 2010 32Tusharadri Sarkar

MiscellaneousMiscellaneous

Where are your commands resting?

> which <command>

> whereis <command>Read a file without opening it:

> cat <filename>Finally, the grand “Manual” of Linux:

> man <item>

The <item> list is really large!! Try it...June 28, 2010 33Tusharadri Sarkar

Thank You !!Thank You !!

34

a quick introduction to linux

Self Improvement

grep grep

file file

tusharadri sarkar note

file searching grepfile

file searching findfile

file searching lsfile

x file

power of grep