LAMP Chapter2 New

8/14/2019 LAMP Chapter2 New

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FOSS / LAMPFOSS / LAMP

Revathi J

Bharathidasan University Technology Park (BUTP)Bharathidasan University


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Standard Files Linux provides three I/O channels to processes.

Standard input, Standard output & Standard error.

Keyboard

Program

Standard Output

Standard Error

Standard Input


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Standard I/O and Pipes Linux supports shell redirection operators allow

standard I/O channels to be redirected to or from

a file.

The following common redirection operators;,

2>,|.


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Redirection Input : '


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Redirecting output Command

The "greater than" symbol '>' is used for save theoutput.

Example :$ ls -l > outputfile

If you want to add or append the date to thisoutput file, use the command:

$ date >> outputfile

with two "greater than" symbols (>>) we will addor append to the file without erasing its contents.


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The command 2> symbol is used for creating afile for an error message that you may get.

You can redirect the standard error into some file.

Example$ find / -name resolv.conf 2> errorfile

To display the contents of the errorfile,

$ cat errorfile

Redirecting Standard Error


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Pipe | command

This symbol is like two vertical slashes, one on topof the other.

That means that the pipe will separate two

commands so that they will be done one after theother.

Example$ ls -l /proc$ ls -l /proc | more Scroll down with the ENTER key$ ls -l /proc | less Scroll with arrows/pgup/pgdown


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Tee command

Lets you tee a pipe: redirect output to a file whenstill piping it to another program.

Example

$ set | tee set.out | less

The output from set is written to file set.out whilealso piped to less

Tee is useful to save the output at various stagesfrom a long sequence of pipes.

Example

$ | tee file1.out | sort | tee file2.out


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Cat Command Contents of the files are displayed sequentiallywith no break.

Files display concatenated.

Syntax$ cat [options] [file...]

Example$ cat /etc/profile$ cat /etc/profile | /etc/passwd >> output.txt

$ cat /etc/profile | tee out.txt


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The Linux Security Model

Users and groups are used to controlaccess to file and resources.

Users log in to the system by supplyingtheir user name and password.

Every file on a Linux system is owned by auser and associated with a group.

Every process has an owner and groupaffiliation, and can only access theresources its owner or group can access


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Users

Every person t at ogs nto t e computer sconsidered to be a user.

Every user has a unique User ID number (the uid)

User names and uids are stored in /etc/passwd file.

User have full access to their home directories.

Users can not change or even read eachother's files without being given permission.


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Groups Users are ass gne to groups w t un que group ID

numbers (the gid). All users in a group can share filesthat belongs to the group.

A users primary group is defined in the/etc/passwd file and secondary groups (gids) aredefined in the /etc/group file.

Primary group can be changed using the newgrpcommand: # newgroup othergroup

where othergroup is one of the userssecondary groups.


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Root User

The root user has special administrative

account sometimes called the superuser

root has complete control over the system

To protect the system from accidentaldamage, it is important for systemadministrators to use a normal user accountfor as much work as possible.


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Linux File SecurityEvery file and directory has permissions set thatdetermine who can access it.

Permissions are set for :Owner of the fileGroup membersAll others

Permissions that are set are calledRead,write andexecute permissions.


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Permission TypesFour symbols are used when displayingpermissions:

r permission to be read a file orlist a directorys contents.

w permission to be write a file orcreate & remove files from a directory.

x permission to be execute a program orchange into a directory and do a longlisting of the directory.

- no permission


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Examining Permissions File permissions may be viewed using

$ ls -l /bin/login

-rwxr-x-r-x 1 root root 19080 Apr 1 18:30 /bin/login

Directories permissions may be viewed using

$ ls -l /bin

drwxr-x-r-x 2 root root 4096 Apr 15 18:30 /bin

File type and file access permissions aresymbolized by a 10 character string


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Interpreting Permissionsdrwxr-x-r-x 2 root root 4096 Apr 15 18:30 /bin

The 1 Character is used to distinguishesdirectories (d) from regular fiels (-).

- regular file, d directory, l symbolic link, b block special file, c character special file,p named pipe, s - socket

Characters 2,3 and 4 identify permissions for the

owner(u).

Characters 5,6 and 7 identify permissions for thegroup(g).

Characters 8,9 and 10 identify permissions for allothers(o).


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Linux Process SecurityW en a process accesses a i e, t e user an group

of the process are compared with the user andgroup of the file.

If the user matches the user permission apply.

If the group matches, but the user doesn't, the

group permissions apply. If neither match, the other permissions apply.


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Changing Permissions The permission instruction can be issued either

symbolically or numerically.

The chmod command changes permission of filesand directories.

Who may be chosen from Operator may be Permission may bechosen from chosen from

u owner of the file + Set permission r readg group - Unset permission w writeo others = Assign a permission x executea all three categories s set user ID bit or

group ID bitt sticky bit

(for directory)


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Symbolic Method Examples

# chmod u+w,go-w txtfile// grants write access to owner but denies to groupand others.

# chmod u=rw txtfile

// Sets user permissions to read and write, with executeturned off, regardless of the current permission.

# chmod +r txtfile// Makes the file world-readable.


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Numeric Method To change the permission on a file the numeric

method is easier than the symbolic method.

Uses a three digit mode number first digit specifies owner permission second digit specifies group permission third digit specifies others permission

Permissions are calculated by adding: 4 read 2 write 1 execute 0 no permission


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Numeric Method - Examples # chmod 664 file

// Read and write set for owner and group, read-only for others. # chmod 660 file

// Read and write set for owner and group, no permission forothers.

# chmod 444 file// Read-only permission set for all.

With directory permissions: # chmod 755 dir

// Full permission set for owner, read and execute setfor group and others.

# chmod 770 dir// Full permission set for owner and group, nopermission others.

# chmod 555 dir

// Read and execute permission set for all.


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Advanced Topics in Users, Groups & Permissions

All authentication is stored in plain text files:

/etc/passwd/etc/shadow/etc/group

The /etc/passwd file contains seven fields. Username, password, uid, gid, GECOS field, homedirectory, and shell to be run when a user logs in.

root:x:0:0:root:/root:/bin/bash


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The /etc/shadow file is referenced when someonelogs in: the file contains a mapping of a user nameto a password.

The /etc/shadow file contains user name,password encryption, days from linux started,minimum days, maximum days, warning days.

root:!!:13326:0:99999:7:::!! - refers password lock.


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Changing your identityThe su command is used to change identities.

To start a new shell as a different user:# su # su -

Lets suppose jack has bob permission to read hisemail. He can temporarily assume jack user id:

$ su bobpassword:

$ whoami bob


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User Information Commands The information commands provide the

information about the users.

Example, Find out who you are

whoami Find out what groups you belong to

groups, id Find out who is logged in

users, who, w Find login/reboot history

last


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Default permissions and UmaskDe au t permission or i es is 666Default permission for directories is 777

umask is subtractor from default to determine newfile/directory permissions

non-privileged users umask is 002

files will have permissions of 664 directories will have permissions of 775

roots umask is 022


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Special permissions A fourth permission set (in addition to

user/group/other) Applicable in four cases:

Set user ID or suid for an executable Set group ID or sgid for an executable Set group ID or sgid for a directory Sticky bit for a directory

Use the chmod command, preceding the usualthree digits with a digit representing thespecial permission : 4 for suid, 2 for sgid, 1 for the sticky bit.

Example:# chmod 3775 groupdir


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Special Permissions for Executables

e et erm ss on

Suid : Command run with permissions ofthe owner of the command, not exexcutorof the command

In long listing, the suid permission isdisplayed as a lower case s where the x

would otherwise be located for the userpermission.

$ chmod 4551 passwd$ ls -l passwd

-r-s- -x- -x 1 root root 15367 May 20 2007 passwd


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Set gid command sgid : command runs with group affiliation of the

group of the command:

$ chmod 2551 passwd $ ls -l passwd

-r-xr-s- -x 1 root john 30899 Aug 18 passwd


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Special Permissions for Directories

Sticky Bit

Files and directories with the sticky bit set can onlybe removed by the owner and root, regardless of thewrite permissions of the directory

$ chmod 1777 /tmp

$ ls ld /tmpdrwxrwxrwt 30 root root 7089 Mar 9 10:28 /tmp


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sgid : files created in directories with the sgid bitset have group affiliations of the group of thedirectory.

This is commonly used on group directories:

$ chmod 2770$ ls l groupdir

drwxrws- - - 2 john eric 4089 Mar 9 10:20 groupdir

Often both the sticky bit and the sgid permissionwill be set on a group directory


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Vi Editor

vi : the 'visual editor', standard Linux and Unix editor.

Let's make a text file. Type: vi textfile

Three modes in vi editor, Command mode

Cursor movementChange, delete, yank, put and search

Insert mode

Type in new textReturn to command mode with Ex mode

Configuring, exiting, savingSearch and Replace

To enter ex mode, type : while in command mode


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Common vi editor command listFor this Purpose Use this vi Command SyntaxTo insert new text ESC +i

To save file ESC +: +w

To quit without saving ESC +: +q!

To save and quit vi editor

ESC +/word

n

To save file with file nam(save as)

ESC +: +w "filename"

ESC +: +wq

To search for specified word inforward direction

To continue with search


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Command list continued....For this Purpose Use this vi Command Syntax

ESC +?word

ESC +p

To delete word from cursor position

To undo ESC +u

To redo

To search for specified word inbackward direction

To copy the line where cursor islocated

ESC +yyESC +4yy

To paste the text just deleted orcopied at the cursor

To delete entire line where cursor islocated

ESC +ddESC +4ddESC +dw


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Partitions and Filesystems n nux, ar s r ves are v e nto

partitions.

These partitions are formatted withfilesystems, and these filesystems are allowuser to store data and access files.

There are different Filesystem types areavailable, the default Filesystem is ext3.Other common filesystems are ext2,msdosand iso9660.


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Symbolic (or Soft) links

A symbolic link points to another file

ls l displays the link name and thereferenced file

To create a symbolic link$ ln -s /etc/passwd password

$ ls - li password /etc/passwd

30338 -rw-r--r-- 1 root root 1729 Aug 24 11:43 /etc/passwd30376 lrwxrwxrwx 1 ram ram 11 Aug 24 10:43 password /etc/passwd


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Hard links One physical file on the filesystem

File is present in the filesystem as long as at least

one link remains.

To create an hard link to an existing file, use theln command:

$ ln txtfile new $ ls -li txtfile new 24567 -rw-rw-rw- 1 ram ram 29 Aug 24 11:43 txtfile 24567 -rw-rw-rw- 1 ram ram 29 Aug 24 11:43 new


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Checking free space df reports disk space usage

Reports total kilobytes, kilobytes used, kilobytesfree per file system

- h displays sizes in easier to read units

$ df /optFilesytem 1K-blocks Used Available Use% Mounted on/dev/hda7 15685 51234 10244 20% /opt

$ df -h /opt

Filesytem Size Used Available Use% Mounted on/dev/hda7 16G 4.9G 11G 20% /opt


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du command du reports disk space usage

Reports kilobytes used per directory Includes subtotals for each subdirectory -s option only reports single directory summay Also takes -h option

Example :$ du -s /dev 11630 /dev


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Removable media Mounting means making a foreign filesystem

look like part of the main tree

Before accessing, media must be mounted.

Before removing, media must be unmounted.

Mountpoints are usually under /media.


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Mounting CDs and DVDs When using X Window System, inserting a CD

into the drive automatically mounts the CDand adds an icon to the desktop.

Otherwise, must be manually mounted, CD/DVD Reader

$ mount /media/cdrom$ umount /media/cdrom

CD/DVD Writer$ mount /media/cdrecorder$ umount /media/cdrecorder

If you want to eject the CD out, you have to

execute the eject command.


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Mounting USB Media When using X Window System, automatically

mounted in Gnome/KDE and icon created incomputer window.

USB disks are treated as SCSI devices, thus theyare referenced as /dev/sda, /dev/sdb, etc.

If you want to mount manually,$ mount /media/$ umount /media/


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Compression Utilities gzip, gunzip

Standard linux compression utility Up to 75% compression for text files

# gzip v file# gunzip file.gz

bzip2, bunzip2 newer Linux compression utility Generally archieves better compression than gzip.

# bzip2 -v file# bunzip2 file.bz2


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String Processing - head The head command displays first few lines of the

text in a file. (i.e) it display from top of the file.

Example: # head n 3 /etc/passwd root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:

daemon:x:2:2:daemon:/sbin:

-n or --lines specifies the number of lines todisplay.


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tail The tail command displays last few lines of the

text in a file. (i.e) it display from bottom of thefile.

Example: # tail -n 2 /etc/passwd ntp:x:38:38: :/etc/ntp:/sbin/nologin

gdm:x:42:42: :/var/gdm:/sbin/nologin

-n or --lines specifies the number of lines todisplay.


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wcwc - word count is used to count lines and

characters.

Example: # wc text.txt 20 200 1500 text.txtl - for line count

w - for word countc - for character count


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grep grep general regular expression processor,

displays the lines in a file that match a pattern. Itcan also process standard input.

# grep eric /etc/passwd eric:x:501:501:eric:/home/eric:/bin/bash

# ls | grep d*

# grep [Dd]og testfile -it displays either the string Dog or

the string dog from the file testfile.


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find Finds one or more files assuming that you know

their approximate filenames. Syntax: $ find -name

Examples: $ find / -name 'myhome.html'

In the above command the system would search forany file named myhome.html in the currentdirectory and any subdirectory


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Investigating and Managing Processes Process :

It is an executing program with several components and

properties.

pstree shows the process ancestry for all processrunning on the system.

# pstree

ps displays processes information


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Viewing Processes ps displays processes information # ps -[option]

ps -a processes by all users ps -x processes from all terminals ps -u show process owners

ps -w

include command arguments ps -f show process ancestry ps -l long listing ps -A to see all the process


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Scheduling the process Comman s wi e execute at t e time in icate .

The output is mailed to the user.

Syntax:

# at Example

# at 8:30pm July 10> ls l


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# atq // list the current at jobs

pending.# atrm [jobID] // used to remove pending at jobsTo see the job result, # mail // used to view the executed

jobs


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Scheduling Periodic Processes cron The cron mechanism allow processes to be invokedperiodically.

Syntax:

# crontab [-u user] file# crontab [-l | -r | -e] [username]l - used to display the crontab filer - used to remove the crontab filee - used to edit the crontab file


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A users crontab may look like the following:

# crontab -eu root

#Min Hour DoM Month DoW Command0 4 * * * find / -name passwd0 0 31 10 * echo Welcome to BUTP*/1 11 * * * ls

: wq

For activate the crontab,# service crond restart# chkconfig crond on


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Installing Application Most of the linux application that you want to install

are available in RPM format.

To install an RPM archive file with the rpm command,use the following syntax;

# rpm i [option] package

The options:--v - to get more verbose feedback, along with

some of the output.-h - Prints 50 hash marks(#) as the package is

unpacked.


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Querying packages

Querying Packages

Using the query options (-q) of rpm, you can getinformation about RMP package.

# rpm -qalist all the installed packages


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Thank You


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Command list continued ....For this Purpose Use this vi command Syntax

Go to the first line in the file ESC +g

Go to the last line in the file ESC +G

ESC +1G or H

Go to middle line on screen ESC +M

Go to last line on screen ESC +L

ESC +:$s/word-to-find/word-to-replace/cg

ESC +:!shell-command For e.g. :!pwd

Go to first line in file(any number can be givenand cursor will jump to that line)

Go forward one full screenGo back one full screenGo down half a screen

Go up half a screen

To Find all occurrence of given word andReplace then globally without confirmation

ESC +:$s/word-to-find/word-to-replace/g

To Find all occurrence of given word andReplace then globally with confirmation

To run shell command like ls, cp or date etc

within vi


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InodesAn inode table contains a list of all files in an ext2

or ext3 filesystem.

An inode (index node) is an entry in thetable, containing information about a file(the meta data), including : File type, permissions, link count, UID, GID The file's size and various time stamps Pointers to the file's data blocks on disk Other data about the file


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Inode - example

$ ls -il

80777 -rw-r----- 1 ram ram 5120 Sep 11 12:50 txtfile59907 drwxrw---- 2 ram ram 4098 Sep 11 12:50 data80787 -rw-r----- 1 ram ram 1500 Sep 11 12:52 file

The inode value is showed in the first column


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cp and inodeWhen a file is copied to a new name in the same

directory, the directory and the inode table get anew entry.

Example: $ ls - li txtfile 24567 -rw-rw-r-- 1 ram ram 26 Sep 25 20:16 txtfile

$ cp txtfile new 24567 -rw-rw-r-- 1 ram ram 26 Sep 25 20:16 txtfile 24568 -rw-rw-r-- 1 ram ram 26 Sep 25 20:16 new


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mv and inodeWhen a file is moved, the inode number remains

the same.

The data on the file system is not moved.Example: $ ls - li txtfile

24568 -rw-rw-r-- 1 ram ram 26 Sep 25 20:16 txtfile $ mv txtfile new

$ ls - li txtfile new 24568 -rw-rw-r-- 1 ram ram 26 Sep 25 20:16 new


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cut cut is used to cut fields or columns of text from

a file and display it to standard output.

Example: # cut -f3 -d: /etc/passwdWill display a list of uids from /etc/passwd,because uids are stored in field three and : is

used as a delimiter. # cut -c2 -5 /etc/passwd

It will display character starting from 2nd andending with 5th character.


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paste paste combines files horizontally. It takes a line

from each file and paste them together tostandard output, separated by a tab.

Use the d option to change the output delimiter. # paste -d: test1 test2 > mergefile

It takes the line from each file (test1 and test2)and put it into the output file.


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uniq Theuniq removes duplicate lines from a file.

Example# vi uniqfile

Sunday Monday

Tuesday Sunday Friday Monday

# uniq uniqfile

Sunday Monday Tuesday Friday


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Sort Sorts text to stdout original file unchanged

By default sort sorts the file in ascending order using

the entire line as a sorting key.

Syntax:# sort [option] filename

-r reverses sort-n numeric sort-u unique (remove duplicate lines in output)


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tr tr is used to translate characters; that is given two

ranges of characters, any time a character inrange 1 is found, it is translated into the

equivalent character in range 2.

# tr a-z A-Z < testfile

The translated output is stored into testfile.


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diff Diff is used to compare the contents of two files

for differences.

# diff test1 test2

< This is test file // first file test1 -------

> Welcome // second file test2


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Specll check aspell is an interactive spell checker. It offers

suggestions for corrections via a simple menu-driven interface.

# aspell check testfile aspell -l will non-interactively list the misspelledwords in a file read from standard input.

# aspell -l < stdfile


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look A quic spe ing ictionary oo up can e

performed with look. It comes in handy when you need the spelling of a

word of which you know the first few letters.

# look le Leave

Letter Lead Least

.


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Regular Expressions Regular expressions are pattern matching engine sed - stream editor. It will perform a search and

replace on all lines in the file, sending the modifieddata to standard output; that is, it does not actually

modity the existing file.

# sed [sting] Example:

# sed s/cat/dog/ pets// cat being replaced by dog string. # sed s/cat/dog/g pets

// entire cat string being replaced by dog string.

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LAMP Chapter2 New