April 6, 2017 | Author: Saminadane Thiyagarajan | Category: N/A
EMPOWERING SYSTEM ADMINISTRATORS
RHCSA-1
OS
UNIX � It is a complete operating System. � It comes with all the programs such as editor, compilers etc., � It Comes with Various file systems such as AIX, HP UX,Solaris. � It was designed as a multiuser operating system. � Other wellknown operating systems included Windows, Macintosh System 7, and MSDOS.
UNIX Operating System Names: HP-UX IBM AIX SUN SOLARIS MAC OS X IRIX
MINIX (from "mini-Unix"): � It’s a POSIX compliant, Unixlike computer operating system based on a microkernel architecture. NOTE: (Portable Operating System Interface, is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems) � Starting with MINIX 3, the primary aim of development shifted from education to the creation of a highly reliable and selfhealing microkernel OS. � MINIX is now developed as opensource software. GNU/Linux: � The GNU system along with Unix or Linux as it’s kernel make a complete operating system.
LINUX • It’s not a operating system. • It’s a free clone of the UNIX kernel, and like GNU tools has succeeded beyond all expectations. • The kernel (from german kern,means core) is the main component of most computer operating systems; it’s a bridge between application software to the hardware of a computer. • There are also free Unix variants as well, but they are less likely to use GNU tools because of the philosophical differences in code sharing and licensing. • All linux distribution include installation and management tools,gnu Utilities Such as cp, mv , ls and gnu editors.
Linux Distribution Names: �Debian � Ubuntu �Slackware Linux � Suse �Redhat Enterprise � Fedora � CentOS
LINUX DISTROS
LINUX vs WINDOWS S.No.
LINUX OS
WINDOWS OS
1.
Linux is open Source Os.
Windows is not open Source Os.
2.
Linux Os is freely available.
Windows Os is expensive.
3.
All flavors of Linux come from different companies like Red Hat, Debian , Slackware , etc.,
All flavors of windows come from Microsoft.
4.
Linux can boot from primary partition or logical partition inside an extended partition.
Windows must boot from the first hard disk and must boot from a primary partition.
5.
Linux is multiuser system.
Windows is single user system.
6.
Super user is root (/).
Super user is Administrator.
7.
Linux files names are case sensitive.
Windows files names are not case sensitive.
8.
Linux uses ext2,ext3,ext4 and xfs file systems.
Windows Uses FAT12,FAT16,FAT32 and NTFS file Systems.
BOOTING � Booting is a process or set of operations that loads and hence starts the operating system, starting from the point when user switches on the power button.
BIOS • BIOS stands for Basic Input/Output System • Performs some system integrity checks (POSTPower On Self Test) • Searches, loads, and executes the boot loader program. • It looks for boot loader in floppy, cdrom, or hard drive. You can press a key (typically F12 of F2, but it depends on your system) during the BIOS startup to change the boot sequence. • Once the boot loader program is detected and loaded into the memory, BIOS gives the control to it. • So, in simple terms BIOS loads and executes the MBR boot loader.
MBR MBR stands for Master Boot Record. � It is located in the 1st sector of the bootable disk. Typically /dev/hda, or /dev/sda � MBR is less than 512 bytes in size. This has three components:
�
� primary boot loader info in 1st 446 bytes, � partition table info in next 64 bytes(16,16,16,16) 4 partitions, � magic numbers as mbr validation check in last 2 bytes.
� It contains information about GRUB (or LILO in old systems). � So, in simple terms MBR loads and executes the GRUB boot loader. * Note: A boot loader is the first software program that runs when a computer starts. It is responsible for loading and transferring control to the operating system kernel software (such as the Hurd or Linux). The kernel, in turn, initializes the rest of the operating system (e.g. GNU).
GRUB � GRUB stands for Grand Unified Bootloader. � It is a Multiboot boot loader. � If you have multiple kernel images installed on your system, you can choose which one to be executed. � GRUB displays a splash screen, waits for few seconds, if you don’t enter anything, it loads the default kernel image as specified in the grub configuration file. � GRUB has the knowledge of the filesystem (the older Linux loader LILO didn’t understand filesystem). � Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link to this). � The following is sample grub.conf of Linux. � As you notice from the above info, it contains kernel and initrd image. � So, in simple terms GRUB just loads and executes Kernel and initrd images.
KERNEL � Once
the control is given to kernel which is the central part of all your OS and act as a mediator between hardware and software.
� Kernel once loaded into to RAM it always resides on RAM until the machine is shutdown. � Once the Kernel starts its operations the first thing it do is executing INIT process.
INIT (initialization) � Looks at the /etc/inittab file to decide the Linux run level. � Following are the available run levels � � � � � �
0 1 2 3 4 5
– – – – – –
halt Single user mode Multiuser, without NFS Full multiuser mode unused X11
� 6 – reboot
� Init identifies the default initlevel from /etc/inittab and uses that to load all appropriate program. � Execute ‘grep initdefault /etc/inittab’ on your system to identify the default run level � If you want to get into trouble, you can set the default run level to 0 or 6. Since you know what 0 and 6 means, probably you might not do that. � Typically you would set the default run level to either 3 or 5.
RUN LEVELS � When the services sendmail from the
Linux system is booting up, you might see various getting started. For example, it might say “starting …. OK”. Those are the runlevel programs, executed run level directory as defined by your run level.
� Depending on your default init level setting, the system will execute the programs from one of the following directories. � � � � � � �
Run Run Run Run Run Run Run
level level level level level level level
0 1 2 3 4 5 6
– – – – – – –
/etc/rc.d/rc0.d/ /etc/rc.d/rc1.d/ /etc/rc.d/rc2.d/ /etc/rc.d/rc3.d/ /etc/rc.d/rc4.d/ /etc/rc.d/rc5.d/ /etc/rc.d/rc6.d/
� Please note that there are also symbolic links available for these directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d. � Under the /etc/rc.d/rc*.d/ directories, you would see programs that start with S and K. � Programs starts with S are used during startup. S for startup. � Programs starts with K are used during shutdown. K for kill. � There are numbers right next to S and K in the program names. Those are the sequence number in which the programs should be started or killed. � For example, S12syslog is to start the syslog deamon, which has the sequence number of 12. S80sendmail is to start the sendmail daemon, which has the sequence number of 80. So, syslog program will be started before sendmail.
LINUX HIERARCHY
� pwd command : It is used to display the present (or) current working directory. Syntax: #pwd Example: # pwd /root � date command : date command is used to print the system date and time. Syntax: # date Example: #date #date s “yyyymmdd hh:mm:ss”
=� To set date and time
� cal command : cal command is used to print the calendar of the current month. Syntax: # cal Example: #cal # cal 3 #cal 2015 � cd command: The following command is used to change from one directory to another directory. Syntax: #cd Example: #cd .. To a directory one level up (parent directory) #cd switch to previous working directory #cd / To the / (slash) directory #cd /root To switch to root directory
� Absolute path:
A complete and full path of a file or folder is called absolute path. A file or folder which begins with under “ / ” is called as absolute path. Example:
# cd /test/team � Relative path: A file or folder which starts without under “ / ” is called as relative path. A shortcut path of file is called relative path. Example: # cd ../team
� ls command: It is used to list the files & folders in a present working directory. Syntax: ls [argument] Options: l a d h R i t Z Example: #ls l /root #ls –ldZ /home
long listing (properties) hidden files & normal files folder properties human readable format recursive in tree structure Inode number sort by time format. display security context of the files
� mkdir command : It is used to create a directory. Syntax: mkdir directory name Options: p parents (To create multiple directories) Example: #mkdir /data /data1 #mkdir p /soft/dvd/os � cat command: It is use to create a file and view the content in the file. Syntax: #cat Example1: # cat > test =� To create the file CTL+d to save the file # cat test =� following command to view the file content #cat >> test =� The following command is used to append a text to the file.
� touch command: It is used to update the time stamps of a file and create an empty file. Syntax: �,
#touch [filename] Example: � cp command:
# touch /test /hp /ibm linux solaris =� To create multiple file on single line command It is used to copy the file or directory (by using Absolute or Relative path)
Syntax: #cp [source] [destination]
Options: a p v r f
archive ( It will not modify the time and date) preserve ( It will not modify file permission) verbose (explain what is being done) recursive (To copy all folder) force (Force to copy)
Example: #cp rvf /root/data /soft/ =� copy command with multiple options
� mv command: The following command is used to move and rename the files and directories. Syntax: #mv
Example: # mv � rm command:
Syntax: Options:
Example:
/root/songs /opt/
# mv /songs /mp3songs
=� To move one location to another location =� To rename the directory or file
The following command is used to remove files. rm i r v
interactive (prompt before removal) recursive (remove directory and their contents recursively) verbose (explain what is being done)
#rm rvf /root/data.txt
� whatis command: It searches the short manual page descriptions in the whatis database for each keyword & and print a oneline description to standard output for each match. Syntax: Example: � info command: Syntax: Example: � man command:
#whatis # whatis mv It is used to provide the full information about the command. #info command #info mkdir
It is used to view online manual pages of any command. Almost every command has a man “page”. Syntax: Example:
#man command # man cp
� history Command: It is used d to view list of used commands. Syntax: #history [options] Options :
c
=� clear (Clear the history)
Example: #history #history c � Echo: It is used to display the set of characters in the terminal window. And it is widely used in scripting language in linux. Syntax: Example:
echo ‘arguments’ #echo “my company name is sysadmin” #echo $HOSTNAME #echo $SHELL #echo $HOME
� head command: It is used to view first ten line of the file content. Syntax: #head [options] Options : Example:
#head /etc/passwd #head 5 /etc/passwd
� tail command: It is used to view last ten line of the file content. Syntax: #tail [options] Options : Example:
#tail /etc/passwd #tail 5 /etc/passwd
� sort command: It is used d to view the file content in ascending and descending order. Syntax:
#sort [options]
Options : f r Example:
( ascending order ) ( descending order )
#sort f /etc/passwd #sort r /etc/passwd
� less command: It is used d to view the file one page at a time. Syntax: #less Example:
#less /etc/passwd
� more command: It is used d to view the big file little by little. Syntax: #more Example: � cut command: Syntax:
#more /etc/passwd it is used to get particular field, column or character. #cut [options]
Example:
#cut d : f1 /etc/passwd [option is delimiter (i.e) separated by “ : “ ] #cut c 26 file.txt [ Character 2 to 6 only display ] � nautilus command: It is used to view the files & folders in a graphical browser. Syntax: nautilus [directory name] Example: # nautilus /mnt/
rsync command: It is used to synchronize faster, flexible replacement for rcp. Syntax: rsync [src HOST] [des HOST] Example: rsync test
[email protected]:/home/tom scp command: It is used to copies the files between hosts on a network. It use for data transfer & uses the same authentication & provides the same security as SSH. Syntax: scp host1 host2 Example: scp –r data
[email protected]:/home/tom
GREP � Grep stands for Global search for Regular Expressions and Print. � Most of us use grep just for finding the words in a file. � The power of grep comes with using its options and regular expressions. � You can analyze large sets of log files with the help of grep command. � Syntax: grep [options] pattern [list of files] � Examples: !grep grep "Error" logfile.txt grep i "UNix" file.txt grep "^[09].*" file.txt grep v "^$" file.txt
Running the last executed grep command Search for a string in a file Case insensitive search Specifying the search string as a regular expression pattern. Displaying the nonempty lines
FIND � Find is one of the powerful utility of Unix (or Linux) used for searching the files in a directory hierarchy. � Syntax: find [conditions] [pathnames] � Examples: !find (last executed find command) find name "sum.java“ (file using name) find iname "sum.java“ (using name and ignoring case) find /etc name "*java*“ (files in a specific directory) find mindepth 2 maxdepth 5 name “sum.java” (files in the subdirectories between level 1 & 4) find . type s (or) d (or) f (Finding socket files (or) dir (or )files) find type d name ".*“ (Finding hidden directories) find . type f name ".*“ (Finding hidden files) find . perm 777 (files based on the file permissions) find . size 1M(or)+1M(or)1M (files size is exactly 1M/large/small) find . type d (or) f empty –delete(remove empty dir (or)files) find . mmin 30 (modified 30 minutes back) find . mtime 1 (modified 1 day back)
Vi & Vim
�This "vi" tutorial is intended for those who wish to master and advance their skills beyond the basic features of the basic editor. It covers buffers, "vi" command line instructions, interfacing with UNIX commands, and ctags. The vim editor is an enhanced version of vi. The improvements are clearly noticed in the handling of tags. � The advantage of learning vi and learning it well is that one will find vi on all Unix based systems and it does not consume an inordinate amount of system resources. Vi works great over slow network ppp modem connections and on systems of limited resources. One can completely utilize vi without departing a single finger from the keyboard. (No hand to mouse and return to keyboard latency) � NOTE: Microsoft PC Notepad users who do not wish to use "vi" should use "gedit" (GNOME edit) or "gnp" (GNOME Note Pad) on Linux. This is very similar in operation to the Microsoft Windows editor, "Notepad". (Other Unix systems GUI editors: "dtpad", which can be found in /usr/dt/bin/dtpad for AIX, vuepad on HP/UX, or xedit on all Unix systems.)
Start Vi or Vim
Command Mode
Enter Insert Mode
:w q!
Esc
Back to command mode
Insert mode
Press a,I,o,Ins
There are three types of mode � � �
Insert Mode Command Mode Execute Mode
�Insert mode - inserting/appending text
�Cut, Paste and delete
� i - insert before the cursor � I - insert at the beginning of the line � a - insert (append) after the cursor � A - insert (append) at the end of the line � o - append (open) a new line below the current line � O - append (open) a new line above the current line � ea - insert (append) at the end of the word � Esc - exit insert mode
� yy - yank (copy) a line � 2yy - yank (copy) 2 lines � yw - yank (copy) word � y$ - yank (copy) to end of line � p - put (paste) the clipboard after cursor � P - put (paste) before cursor � dd - delete (cut) a line � 2dd - delete (cut) 2 lines � dw - delete (cut) word � D - delete (cut) to the end of the line � d$ - delete (cut) to the end of the line � x - delete (cut) character
�Parameters � � � � � � � � � � �
:set list Show invisible characters :set nolist Don’t show invisible characters :set number Show line numbers :set nonumber Don’t show line numbers :set autoindent Indent after carriage return :set noautoindent Turn off autoindent :set showmatch Show matching sets of parentheses as they are typed :set noshowmatch Turn off showmatch :set showmode Display mode on last line of screen :set noshowmode Turn off showmode :set all Show values of all possible parameters
�Search and replace � /pattern - search for pattern � ?pattern - search backward for pattern � n - repeat search in same direction � N - repeat search in opposite direction � :%s/old/new/g - replace all old with new throughout file � :%s/old/new/gc - replace all old with new throughout file with confirmations �Exiting � :w - write (save) the file, but don't exit � :wq or :x or ZZ - write (save) and quit � :q - quit (fails if there are unsaved changes) � :q! or ZQ - quit and throw away unsaved changes
User & Group Management �
Files and Directories for user
�
Password File Format
�
User Management
�
Password Aging
�
Group Administration
�
Switching Accounts
�
Sudo
�
GUI Tool for user management
Files & Directories for user 1. Basic files for user & groups /etc/shadow
Secure user account information
/etc/passwd
User account information
/etc/gshadow
Contains the shadowed information for group accounts
/etc/group /etc/sudoers
Define the groups to which user belong List of who can run what by sudo
2. User Environment Files and Directory /etc/skel
files and directories automatically copied over to new user's home directory
/etc/default/useradd useradd defaults file /etc/login.defs
define the sitespecific configuration for the shadow password suite.
/etc/profile
controls systemwide default variables such as export variables. File creation mask(umask). Terminal types, Mail messages
~/.bash_profile
execute to configure your shell before the initial command prompt.
/etc/bashrc
interactive nonlogin shell started at the commandline using a shell program such as /bin/bash or /bin/sh. Executed by ~/.bashrc
Password file Format 1.
Passwd File Format ( /etc/passwd ) sami:x:501:501::/home/sami:/bin/bash
username
password
uid gid Description Home directory Login shell
Password, X=reference to /etc/shadow, empty=no password, *or !=no login possible
2.
Shadow File Format ( /etc/shadow ) sami:$6$i7.SAQK2$U9dSrT4E9tEoLEBfS:16729:0:99999:7:::
1. 2. 3. 4. 5. 6. 7. 8. 9.
1
2
3
4
5
6
User name: your login name Password : encrypted password. “$1$” stands for MD5, “$2a$” is Blowfish, “$5$” is SHA256 and “$6$” is SHA512. Last password change: When was the password last changed. Minimum: The minimum number of days required between password change i.e the number of days left before the user is allowed to change his/her password. Maximum: The maximum number of days the password is valid ( after that user is forced to change his/her password) Warn: number of days before password is expire that user is warned that password must be changed Inactive: The number of days after password expire that account is disabled Expire: When was that account is disabled. i.e an absolute specifying when the login may no longer be used. Special flag: This field is reserved for further use.
User Management 1. Useradd add new user a. Adding new user #useradd user1 b. List default setting #useradd D #useradd D s /bin/sh //change default shell c. Supplementary groups #useradd G mail user2 d. Home Directory #useradd d /home/samihome user3 e. Change skel directory #useradd –m k /etc/skel2 user4 f. Specific shell #useradd s /bin/sh user5 // /etc/shells g. Specific uid #useradd u 550 user6 h. Account expire #useradd –e 2015/10/30 user7
2. Usermod modify user’s data a. Shell and directory change #usermod s /bin/csh d /home/samihome m tom b. Login name change #usermod l nathan (new) tom(old) c. Lock and unlock user #usermod L tom //lock #usermod U tom //unlock d. New UID #usermod u 510 tom e. Expire date #usermod e 2015/11/30 tom #usermod e “” tom //remove expire date 3. Userdel delete user a. Delete user and leaving home directory #userdel tom h. Delete user with home directory #userdel –r tom
4. Pwconv & pwunconv : combine or separate /etc/passwd and /etc/shadow #pwconv #grep root /etc/shadow #pwunconv #grep root /etc/shadow ; grep root /etc/passwd #ls -l /etc/passwd /etc/shadow 5. Creating password for user a. Passwd #passwd tom #passwd -S tom // To check the passwd status of user account 6. Password lock and unlock for user #passwd -l tom #passwd -u tom 7. Login without password - empty field #grep tom/etc/shadow tom::16729:0:99999:7:::
8. Blocking login by emergent situation #vi /etc/nologin Under system checking currently Please login again after 20:00!!! 9. Listing user information #finger –l tom 10. How to monitor user a. Monitor file • /var/run/utmp : keeps track of the current login state of each user. • /var/log/wtmp : records all login and logouts history. • /var/log/btmp : records failed login attempts. b. Monitoring command Show who is logged on and what they are doing. #whoami Reports the most recent login of all users or of a given user from /var/log/lastlog #lastlog Contains all the bad or failed login attempts. #lastb Show who is logged on #who
PASSWORD AGING
1. By defaults passwords do not expire 2. Forcing passwords to expire is part of a strong security policy 3. Modify default expiration setting in /etc/login.defs •PASS_MAX_DAYS 99999 •PASS_MIN_DAYS 0 •PASS_MIN_LEN 5 •PASS_WARN_AGE 7 4. Chage - to modify password aging a. Chage [-m mindays] [-M maxdays] [-d lastday] [-I inactive] [-E expiredate] [-W warndays] user b. List user’s current setting #chage –l tom
c. Set Password Expire Date for an user chage option –M #chage –M 10 tom d. Password Expire Warning message during login #chage –W 5 tom e. Set the Account Expire Date for an User #chage –E “2015-11-30” tom f. Force the user account to be locked after X number of inactivity days #chage –I 10 tom g. How to disable password aging for an user account #chage –m 0 –M 99999 –I -1 –E -1 tom #chage –l tom
GROUP ADMINISTRATION 1. Group Administration • A user can be participant to more than one group at the same time. • A user who is member of a group can change to that group without password but a user NOT member can only change to that group password exit and the user gives it. • One or more user can become group administrator for specific groups. • Group Administrator can:
1. Add/change/delete the password of the group 2. Add/delete users to the group 3. Reserve the group to member-only. 2. Types of group
Primary group
every user must be a member of at least one group, which is identified by the numeric GID in /etc/passwd
Secondary group
A user may be listed as member of additional groups in the relevent entries in the /etc/group
User private group
Created whenever a new user is added to the system and has the same name as the user for which it was created
Example: [sami@server~]$id Uid=501(tom) gid=502(tom) groups=502(tom),506(admin)
3. Group management commands a. groupadd – adding group #groupadd admin #groupadd –r admin #groupadd –g 600 HR
//start group id 101 and increase up to GID 499
b. groupmod – modifying group #groupmod [-g newgid] [-n new name] group #groupmod –g 600 –n manager admin c. groupdel – deleting group #groupdel HR d. gpasswd – administer /etc/group and /etc/gshadow #gpasswd admin //making new password for admin #gpasswd –A tom admin //administrator of admin #gpasswd –R admin //restrict non-member login #gpasswd –r admin //delete group passwd #gpasswd –a user1 admin //adding group member #gpasswd –d user1 admin //deleting group member
SWITCHING ACCOUNTS 1.
Su
a. Syntax su [-] [user] su [-] [user] –c command b. Allows the user to temporarily become another user in command line c. Default user is root d. The – option makes the new shell a login shell e. Most systems log the use of su to change to the root account 2. Example •$su •$su – •$su – tom •$su –l tom
SSH stands for secure shell. #yum install openssh* y #service sshd start #chkconfig sshd on #service sshd status #ssh (ipaddress of target pc) #ssh user@(ipaddress of user) #ssh X user@(ipaddress of user with graphical) How to give banner warning at the time of SSH login #vim /etc/issue.net Dont enter to my system..! #vim /etc/ssh/sshd_config Banner /etc/issue.net #service sshd restart
To change SSH port: #vim /etc/ssh/sshd_config Port 3434 #service sshd restart #vim /etc/ssh/sshd_config #PermitRootLogin yes (remove # and permit root login yes or no) #service sshd restart #vim /etc/ssh/sshd_config #PasswordAuthentication yes (remove # and permit password auth yes/no) #service sshd restart #vim /etc/ssh/sshd_config AllowUsers user2 or AllowUsers user2@IP DenyUsers user1 #service sshd restart
SUDO 1. Sudo a. Purpose: to delegate root privileges to non-root users. b. Users listed in /etc/sudoers execute commands with � An effective user id of 0 �A group id of root’s group c. An administrator is contacted if a user not listed in /etc/sudoers attempts to use sudo
2. Example a. Default Syntax
User
MACHINE=COMMANDS
b. Allow root to run any commands anywhere
root
ALL=(ALL)
ALL
c. Allows members of the ‘sys’ groups to run networking, service management apps
%sys
ALL=NETWORKING, SERVICES, DELEGATING, PROCESSESS
d. Allows people in group wheel to run all commands
%whell ALL=(ALL)
ALL
e. Same thing without a password
%whell ALL=(ALL)
ALL
f. Allows member of the users group to mount and unmount the cdrom as a root
%users
ALL=/sbin/mount /mnt/cdrom, /sbin/umount /mnt/cdrom
3. How to use sudo a. Set up sudo Environment in /etc/sudoers as group member %whell ALL=(ALL) ALL #usermod –G 10 tom tom$froups b. Executing a command as super user $sudo mount /dev/cdrom /media/cdrom c. If forgot to give sudo for root command, do it again using !! $head –n 4 /etc/sudoers $sudo !! d. Get Root Shell Access using Sudo $sudo bash; id e. Sudo logging Defaults logfile=/var/log/sudolog #touch /var/log/sudolog $sudo ls /
GUI Tool for User Management
1.
Package checking
#rpm –qa | grep system-config-users
2. Package installation #yum install system-config-users
3. Using GUI tool #system-config-users& •Making new user •Making new group
File Permissions �Umask : umask is the value with this umask mask value kernel can identify who is going to create a file or directory. Umask is the command to find out umask value root users umask 022 normal users umask 002 Example 1: $ umask 333 $ umask 0333 File - 666 – 0333 Directory - 777 – 0333
=> 333 => 444
=>-w- -w- - w => dr - -r - -r - -
Example 2: $ umask 777 $ umask 0777 File - 666 – 777 Directory - 777 – 777
=> 000 => 000
==> - - - - - - - - - ==> d- - - - - - - - -
�Chmod command: It is used to change the permission’s for files and directories. The permission instruction can be issued either
symbolic method numeric method Standard files & directories permission # ls –l -rw- r– r--rwx r-x r-x File permissions is made for three groups of users: The owner of the file. For user => u One of the groups existing on the system. For group => g All other users. For others => o
Options: u g o a + =
-
user who owns the files users in the files group other users all the three categories add a permission remove a permission assign a permission:
Symbolic method : r wx s t -
read write execute or cd set user id bit or group sticky bit
Syntax: chmod u+w, go-w chmod u= rw
Example 1: The following command is used to add a permission for the permission of folder. # chmod u+rwx,g+rw,o+r /songs
Example 2 The following command is used to remove the permission of files. # chmod u-rwx,g-rwx,o-rwx /song.mp3
�Numeric method: File permissions read write execute all
4 2 1 7
read,write read,execute write,execute no permission
Syntax : chmod chmod
=> 6 => 5 => 3 => 0
Example 1: The following command is used to modify the folder permissions. # chmod 755 /movie
Example 2: The following command is used to modify the file permissions. # chmod 755 /movie/movie.avi
� Chown command: It is used to change the ownership of the files & directories. Syntax: chown [argument] Example: The following command is used to change the ownership # chown –R tom data
� Chgrp command: It is used to change group of the file / directories. Syntax: chgrp argument Example: The following command is used to change the group. # chgrp technical /data
Special Permission & ACL � Special Permission : SUID, SGID and Sticky Bit � File System ACLs � Three categories to which file permission apply User, Group, Other
� Three standard permission which may apply:
Permission
Effect on Reguler file
Effect on Directory
r (read)
Contents of the can be read
Content of the directory (file names) can be listed
w (write)
Contents of the can be changed
Any file in directory can be created or deleted
x (executable)
Content of the file can be executed as acommand
Content of the directory can be accessed (dependent on file's own permission)
SUID (set UID): When executable file is run, it executes as the user that owns it, not as the user that ran it. Syntax: chmod u+s chmod u-s
=� sets SUID permission on a file =� removes SUID permission
SGID (set GID): When executable file is run, it executes as the group that owns it. All files created below a directory with SGID bit set inherit the group ownership of the parent directory. Syntax: chmod g+s chmod g-s chmod g+s chmod g-s
=� sets SGID permission on a file =� removes SGID permission for a file =� sets SGID permission on a directory =� removes SGID permission for a directory
Note: Useful for sharing files between users
Sticky Bit: When set on a directory, users with write access to the directory can only files they own in the directory. Syntax: Chmod o+t Chmod 0-t
=� sets the sticky bit on a directory =� removes the sticky bit for a directory
Note: Useful for /tmp and other world-writable directories. Permission
Effect on Reguler file
Effect on Directory
SUID chmod u+s file
File executes as user that owns the file, not No effect the user that ran the file.
SGID chmod u+g file File executes as group that owns the file
Files newly created in the directory have group owner set to match group that owns the directory
"sticky bit" chmod o+t file
Users with write on the directory can only remove file they own, they can not remove files owned by other users
No effect
Access Control Lists Access Control List (ACL) provides an additional, more flexible permission mechanism for file systems. It is designed to assist with UNIX file permissions. ACL allows you to give permissions for any user or group to any disc resource. �
ACLs Commands: setfacl sets an ACL entry on a file getfacl gets the list of ACL entries on a file Syntax: setfacl u:: setfacl g:: getfacl Example: #setfacl –m u:sysadmin:r-x/data #setfacl –m g:admin:rwx /data #setfacl –x u:sysadmin /data #setfacl –b /data
Tar Command Tar is an archiving program created to store, maintain, modify and extract files from an archive file known as a tarfile. A tarfile may be made on a tape drive, however, it is also common to write a tarfile to a normal file. Is most widely used command to create compressed archive files and that can be moved easily from one disk to another disk or one server to another server. Usage and Options
• c – create a archive file. • x – extract a archive file. • v – show the progress of archive file. • f – filename of archive file. • t – viewing content of archive file. • j – filter archive through bzip2. • z – filter archive through gzip. • r – append or update files or directories to existing archive file. • W – Verify a archive file. • wildcards – Specify patters in unix tar command.
1. Create an archive file This is the basic command to create an archive it will not create a compressed archive. Just a plain archive, that puts multiple files together.
# tar -cvf doc.tar /tmp/sysadmin 2. Create compressed archive file Now we are going to create a compressed archive, In order to compress, use the “z” or “j” option for gzip or bzip respectively.
# tar -cvzf doc.tar.gz /tmp/sysadmin (gzip) Note: .tgz is same as .tar.gz
# tar -cvfj doc.tar.bz2 /tmp/sysadmin (bzip2) Note: .tbz and .tb2 is same as .tar.bz2
Difference between gzip and bzip2: bzip2 takes more time to compress and decompress than gzip but archival size is less than gzip. 3. Extracting (untar) an archive To untar or extract a (*.tar) file, just issue following command using option “x” (extract) # tar -xvf dragon_ball.tar
4. Uncompress tar.gz archive file To extract a gzipped tar archive ( *.tar.gz ) use the option “z” for uncompressing a gzip tar archive.
# tar -xvzf doc.tar.gz Extract files to a specific directory or path
# tar -xvzf doc.tar.gz -C /home/sysadmin/ Make sure that the destination directory exists, tar is not going to create the directory for you. 5. Uncompress tar.bz2 archive file Extracting a bzipped tar archive ( *.tar.bz2 ) use the option “j” for uncompressing a bzip2 tar archive. # tar -xvjf doc.tar.bz2 6. Extract a one or multiple files To extract a single file out of an archive just add the file name at the end of the line # tar -zxvf doc.tar.gz "./home/goku.txt" (gzip) # tar -jxvf doc.tar.bz2 "./home/goku.txt" (bzip2) You can also extract more than one file.
# tar -zxvf doc.gz "./home/goku.txt" "./home/gohan.txt (gzip) # tar -jxvf doc.tar.bz2 "./homegoku.txt" "./home/gohan.txt (bzip2)
Wildcards can be used to extract out a bunch of files matching the given wildcards.
# tar -zxvf doc.tar.gz --wildcards "*.txt" (gzip) # tar -jxvf doc.tar.bz2 --wildcards "*.txt" (bzip2) The example above will extract all files with “.txt” extension. 7. Listing the archive content List out the contents of the tar archive and not extract them, use the “t” option. # tar -tvf dragon_ball.tar View the (*.tar.gz) file content without extracting # tar -tvfz doc.tar.gz View the (*.tar.bz2) file content without extracting # tar -tvfj doc.tar.bz2 8. Search content of the archive Use the tar command in combination with the grep search the archive. # tar -tvf doc.tar | grep goku.txt For tar.gz/bz2 files use the “z” and “j” option respectively. Also read Using Grep To Search For Text Patterns
9. Adding a file or directory to an existing archive You can add files or directories to existing archives, without having to create new ones.
# tar -rvf doc.tar trunks.txt Adding a directory to the tar is also similar. # tar -rvf doc.tar /tmp/raj You cannot add file or directory to a compressed archive
10. Verify archive files You can verify the archive file that got created.
# tar -tvfW doc.tar You cannot do verification on a compressed ( *.tar.gz, *.tar.bz2 ) 11. Check the size of an archive file To check the size of any tar, tar.gz and tar.bz2 archive file, use the following command. # tar -czf - doc.tar | wc -c For tar.gz/bz2 files use the “z” and “j” option respectively.
Linux Filesystem Management Part 1 Filesystem Management Chapter 1 Filesystem Management Process Chapter 2 Device Recognition Chapter 3 Disk Partitions Chapter 4 Making Filesystem Part 2 How to use New Filesystem Chapter 5 Filesystem Labels Chapter 6 Mount points & /etc/fstab Chapter 7 Mount & Unmount Chapter 8 Handing Swap files and Partitions
Filesystem Management Process 1.Objectives Upon completion of this unit, you should be able to: Manage virtual memory Add new drives and partitions Mount filesystems How to use new Filesystem 2.Over view: Adding new Filesystems to the Filesystem tree 1)Identify Device: /dev/hda or /dev/sda 2)Partition Device: fdisk, sfdisk, GNU parted, Partprobe 3)Make Filesystem: mkfs, mkfs.ext3, mkfs.ext4, mkfs.xfs, mkfs.vfat 4)Label filesystem: e2lable, tune2fs 5)Create entry in /etc/fstab: mount points, mount, and fsck 6)Mount new filesystem: mount, umount
Device Recognition 1.BIOS – a list of device to start Operating System (CD, hard disk) 2.First sector of the first cylinder at hard disk – Master Boot Record 3.Master Boot Record (MBR) contains: a.Executables code to load operating system – Boot Loader b.GRUB – Grand Unified Boot Loader in Linux systems c.Space for partition tables information, Including: • • • • • •
Hard Disk type – IDE (hda, hdb), SCSI or SATA (sda, sdb) Partition id – Linux swap, Linux , Linux LVM, RAID, DOS Partition type – Primary, Extended and Logical Partition has each size – sector, blocks or cylinders Starting cylinder for partition – 1 cylinder is about 8 MB Number of cylinder for partition
Disk Partition 1.Types of partitions a.Primary Partitions: supports only 4 partitions per drive b.Extended Partitions: one of Primary, includes all Logical partitions c.Logical partitions: permits the definition of more than four partitions 2.Total maximum number of partitions supported by the Kernel: a.63 for IDE drives b.15 for SCSI or SATA drives 3.Why partition drives? a.Containment: security breach, user demand b.Performance: Keeping data together which reduce disk head seek c.Quotas: using specific file partition Recovery: easy backup and recovery
4.Managing Partitions 1)Create Partitions using: a.fdisk – most commonly used partitioning program # fdisk /dev/sda b)sfdisk – more accurate and flexible than fdisk #sfdisk /dev/sda c)GNU parted – advanced partition manipulation ( create, copy, resize, etc.) #parted –l /dev/sda #yum install gparted y ; gparted & 2)Partprobe – /proc/partitions Need to reboot after creating new partition so that kernel reads new partition table Reinitializes the kernel’s inmemory version of the partition table without rebooting again #partprobe #kpartx –a /dev/sda; kpartx –l /dev/sda
Making Filesystems 1.Mkfs – Creating file system Mkfs.ext3, mkfs.ext4, mkfs.xfs, mkfs.vfat, mkfs.msdos Specific filesystem utilities can be call directly #mkfs –t ext4 /dev/sda5 (or) #mkfs.ext4 /dev/sda5 2.mke2fs [options] device #mke2fs –j –L data –b 2048 –i 4096 /dev/sda6 L: filesystem label j: journaling b: block size i: inode per ever 4 kb of disk space
Filesystems Labels 1.e2label – filesystem label a.e2label special _dev_file #e2label /dev/sda5 data; e2label /dev/sda5 b.Mount label=fslabel mount _point #mount LABEL=data /data c.See labels and filesystem type of all devices #blkid 1.Tune2fs – Adjust filesystem parameters Reserved blocks, default mount options, fsck frequency a.View current settings #dumpe2fs /dev/sda5 b.Modify the percentage of reserved clocks #tune2fs –m 10 /dev/sda5 c.Set the default mount options #tune2fs –o acl,user_xattr /dev/sda1 d.Disable mandatory filesystem checks #tune2fs –i0 –c0 /dev/sda5
Mount points & /etc/fstab • 1.Configuration of the filesystem – /etc/fstab #device mount_point FS_TYPE option dump_freq fsck_order • LABEL=/data /data ext3 defaults 0 0 • Device: special device file name or filesystem label • Mount_point: the path used to access the filesystem • FS_type: filesystem type • Options: a commaseparated list of options • Dump_freq: dump frequence: 1=daily, 2=every other day, 0=never dump • Fsck_order: 0 =ignore, 1=first, 29: second third • 2.Used by mount, fsck and other programs 3.May use filesystem volume labels in the device field 4.# mount – a can be used to mount all filesystems listed in the /etc/fstab 5.# mount /dev/sda5 # mount –L /data # mount LABEL=/data
Mount & Umount 1.Mount options device mount_point mount [0 options] [t fs_type] device mount_point a.Denying permission to execute files #mount t ext3 o noexec /dev/sda5 /home b.Mount CDRom image file #mount –t iso9660 o loop /iso/documents.iso /mnt/cdimage c.Each file is owned by a specific UID and GID #mount t vfat o uid=500,gid=510 /dev/sdb /mnt/windows d.Mount filesystem to increase I/O performance by reducing disk access #mount t ext3 o noatime /dev/sda6 /data 2.Unmounting filesystems Umount [options] device | mount_point #umount /data a.Cannot umount a filesystem that is in use b.Use the remount option to change a mounted filesystem’s options atomically #mount o remount,ro /data
Handing Swap files & Partitions • 1.Swap space is a supplement to system RAM 2.Process to create swap file and partitions a.Create swap partition using fdisk #fdisk /dev/sda #mkswap /dev/sda9 #vi /etc/fstab /dev/sda9 swap swap defaults 0 0 #Swapon a ; swapon s; free m • b.Create swap file #dd if=/dev/zero of=/swapfile bs=1024 count=100000 (100Mb) #mkswap /swapfile #vi /etc/fstab /swapfile swap swap defaults 0 0 #swapon a #swapon a; free m
Summary Five steps to control linux filesystems 1.Bios recognition 2.Creating partitions – fdisk, gparted, sfdisk 3.Making filesystems for new partition – mkfs 4.Labeling new partitions – e2label 5.Mounting and using new filesystem – mount, /etc/fstab
In Linux, Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel. Most modern Linux distributions are LVM-aware to the point of being able to have their root file systems on a logical volume. Heinz Mauelshagen wrote the original LVM code in 1998, taking its primary design guidelines from the HP-UX's volume manager. LVM is commonly used for the following purposes:
• • • •
Managing large hard disk farms by allowing disks to be added and replaced without downtime or service disruption, in combination with hot swapping. On small systems (like a desktop at home), instead of having to estimate at installation time how big a partition might need to be in the future, LVM allows file systems to be easily resized later as needed. Performing consistent backups by taking snapshots of the logical volumes. Creating single logical volumes of multiple physical volumes or entire hard disks (somewhat similar to RAID 0, but more similar to JBOD), allowing for dynamic volume resizing. LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, repartitioning, and backup.
• • •
To create a LVM, we need to run through the following steps. Select the physical storage devices for LVM Create the Volume Group from Physical Volumes Create Logical Volumes from Volume Group
Let's find out about our hard disks: #fdisk -l #fdisk /dev/sda Command (m for help): displays the fully qualified host and domain name � hostname i > displays the IP address for the current machine � uname n > Display the HostName for the current machine To Check IP Address � ip a � ifconfig -a � ifconfig eth1 � ifconfig eth1 down � ifconfig eth1 up
Temporary ip Note : Maximum 255 IP address in a single N/W card can assign as alias � i) # ifconfig eth0:0 192.168.6.146 255.255.255.0 � ii) # ifconfig eth0:1 192.168.6.150 255.255.255.0 up � iii) # ifconfig eth0:2 192.168.6.151/24 # service network restart > It will destroy the temporary ip Permonent IP Address � cd /etc/sysconfig/networkscripts/ � ls l | grep ifcfgeth � cp p ifcfgeth0 ifcfgeth0:1 �
vim ifcfgeth0:1 DEVICE=eth0:1 ONBOOT=yes HWADDR=00:0c:29:3e:a7:a4 IPADDR=192.168.6.150 TYPE=Ethernet BOOTPROTO=none NETMASK=255.255.255.0 NAME="System eth0:1"
� � � � � � � � � � � � � �
ifconfig eth0:1 service NetworkManager stop chkconfig NetworkManager on service iptables stop service ip6tables stop chkconfig ip6tables on chkconfig iptables on service network restart ifconfig a watch ifconfig ip addr show ip route show ip 4 addr show ip 6 addr show
� ethtool � #ethtool eth0 > � #ethtool t eth0 online > HW component LAN card is working perfectly or not � #ethtool t eth0 offline � #ethtool i eth0 > driver information � #ethtool s eth0 speed 100 autoneg off � #ethtool a eth0 > Display auto negotiation on or off � #ethtool s eth0
netstat #netstat in #service network restart #ifconfig #setup # cat /etc/hosts #hostname server1.verizon.com ====�To set the hostname temporary To set the hostname permenant [root@server ~]# cat /etc/sysconfig/network NETWORKING=yes HOSTNAME=server.verizon.com To Put DNS entry [root@desktop75 ~]# cat /etc/resolv.conf search example.com nameserver 192.168.0.254
IP FORWARDING Enable ip forwarding on your machine. Temporarily set: # sysctl w net.ipv4.ip_forward=1 [OR] # echo 1 > /proc/sys/net/ipv4/ip_forward Permanently set: # vim /etc/sysctl.conf net.ipv4.ip_forward=1 #vim /etc/sysconfig/network FORWARD_IPV4=true # sysctl p /etc/sysctl.conf [OR] # systemctl restart network.service NOTE: sysctl configure kernel parameters at runtime VERIFICATION: # sysctl a | grep net.ipv4.ip_forward # cat /proc/sys/net/ipv4/ip_forward
To stop ipv6 protocols permanently #vim /etc/sysctl.conf net.ipv6.conf.all.disable_ipv6 = 1 #sysctl p p > Load in sysctl settings from the file specified. Note : To disable a particular network card like eth0 permanently #vim /etc/sysctl.conf net.ipv6.conf.eth0.disable_ipv6 = 1 #sysctl p Note : To disable a particular network card like eth0 Temporary # echo 1 > /proc/sys/net/ipv6/conf/eth0/disable_ipv6 I successfully disabled IPv6 once putting the following lines in /etc/sysctl.conf: net.ipv6.conf.all.disable_ipv6 = 1net.ipv6.conf.default.disable_ipv6 = 1net.ipv6.conf.lo.disable_ipv6 = 1
How to Display Routing Table # route n # netstat rn r option specifies that you want the routing table. n option similer to that route command # ip route list #ifconfig br0:2 192.168.1.63/24 # route add default gw 192.168.1.1 # route n Kernel IP routing table # route del default gw 192.168.0.254 #vim /etc/resolv.conf search example.com #nameserver 192.168.0.254 nameserver 203.145.184.13 nameserver 203.145.184.32 # ping google.com
GUI #systemconfignetworktui (or) #setup Note : Port Information can be seen in the file: /etc/services #cat /etc/services | grep i telnet #yum install telnet* y # telnet 192.168.0.85 22 > port no #netstat an | grep w 22 #netstat ant
>It will gives network statistics(which port number of the server is connected to which port number of client)
[root@localhost ~]# arp Address HWtype HWaddress Flags Mask 192.168.6.1 ether 00:50:56:c0:00:08 C
Iface eth0
PORT FORWARDING SYNTAX FOR RHEL6: ssh L local-port:remote-hostname:remote-port username@hostname SYNTAX FOR RHEL7: #firewallcmd permanent addrichrule='rule family=ipv4 source address=clientIP forwardport port=5243 prfamily=ipv4 sotocol=tcp toport=22' #firewallcmd reload #firewallcmd listrichrules Verfication On Client Machine: #ssh serverIP p 5243
HARDWARE MANAGEMENT dmidecode - DMI table decoder # dmidecode –t dmidecode: an argument 't‘ Type number or keyword expected. Valid type keywords are: bios system baseboard chassis processor memory cache connector slot
The SMBIOS specification defines the following DMI types: Type
Information
Type
Information
0
BIOS
10
On Board Devices
1
System
11
OEM Strings
2
Base Board
12
System Configuration Options
3
Chassis
13
BIOS Language
4
Processor
14
Group Associations
5
Memory Controller
15
System Event Log
6
Memory Module
16
Physical Memory Array
7
Cache
17
Memory Device
8
Port Connector
18
32bit Memory Error
9
System Slots
19
Memory Array Mapped Address
Type
Information
Type
Information
20
Memory Device Mapped Address
31
Boot Integrity Services
21
Builtin Pointing Device
32
System Boot
22
Portable Battery
33
64bit Memory Error
23
System Reset
34
Management Device
24
Hardware Security
35
Management Device Component
25
System Power Controls
36
Management Device Threshold Data
26
Voltage Probe
37
Memory Channel
27
Cooling Device
38
IPMI Device
28
Temperature Probe
39
Power Supply
29
Electrical Current Probe
40
Additional Information
30
Outofband Remote Access
41
Onboard Device
• •
Additionally, type 126 is used for disabled entries and type 127 is an endoftable marker. Types 128 to 255 are for OEMspecific data. dmidecode will display these entries by default, but it can only decode them when the vendors have contributed documentation or code for them. Keyword
Types
bios
0, 13
system
1, 12, 15, 23, 32
baseboard
2, 10, 41
chassis
3
processor
4
memory
5, 6, 16, 17
cache
7
connector
8
slot
9
Keywords can be used instead of type numbers with type. Each keyword is equivalent to a list of type numbers:
Keywords are matched caseinsensitively. The following command lines are equivalent: dmidecode –type 0 type 13 dmidecode type 0,13 dmidecode type bios
CPU Information dmidecode t processor cat /proc/cpuinfo > All the info. about the cpu lscpu cat /proc/cpuinfo | grep processor cat /proc/cpuinfo | grep cores grep "core id" /proc/cpuinfo cat /proc/cpuinfo | grep processor | wc –l cat /proc/cpuinfo | grep core | wc –l nproc Note : The nproc command just prints out the number of processing units available. Note that the number of processing units might not always be the same as number of cores.
Note: can see the usage of your CPU cores using top command. Open a Terminal. Type top. You will see some information about tasks, memory etc. Type 1 to show individual CPU usage Note : you can follow the below steps to install lshw tools, then you can use it 1.wget http://ezix.org/software/files/lshwB.02.14.tar.gz tar zxvf lshwB.02.14.tar.gz cd lshwB.02.14 make && make install
#lshw class processor # grep count processor /proc/cpuinfo # ls /sys/devices/system/cpu/ # cat /sys/devices/system/cpu/kernel_max # cat /sys/devices/system/cpu/offline # cat /sys/devices/system/cpu/possible # cat /sys/devices/system/cpu/present # cat /sys/devices/system/cpu/online
RAM # dmidecode t memory | grep "Type" # dmidecode t 17 | grep i Type # dmidecode t 17 # lshw class memory PCI (Peripheral Component Interconnect) #lspci 00:19.0 Ethernet controller: Intel Corporation 82579V Gigabit Network Connection (rev 05) 1 2 3 4
Field 1: PCI bus slot number (Device ID) Field 2: PCI slot name (Device Name) Field 3: Name of device attached and its manufactured company name.(Device Desc) # lspci vmm | more > mm Dump PCI device data in a machine readable form for easy parsing by scripts. #lspci k > Show kernel drivers handling each device and also kernel modules capable of handling it. #lspci v > Be verbose and display detailed information about all devices. # dmidecode t bios | more # dmidecode t baseboard | more # dmidecode t chassis > cabinet info # lspci tv > your master PCI bus is 00. It is better to use v option with t to get detailed information # lspci m
DISK Information # lspci | grep i scsi or # lspci | grep i sata # lspci | grep i eth # cd /sys/bus/pci # ls cd devices/ # ls # cd 0000:00:19.0 # ls # cat device # cat /proc/scsi/scsi # hdparm i /dev/sda > HDD Model No & Serial NO # free m # lsblk # mount | column t # mount | column t | grep ext # dmidecode | grep ^Handle | wc l # dmidecode | grep structures
To add a HDD # lspci | grep i scsi # cd /sys/bus/pci/devices #ls # cd 0000\:00\:10.0/ #ls Note : open one duplicate terminal and watch #udevadm monitor Note : add a HDD in virtula server then scan #fdisk l # echo " " > /sys/class/scsi_host/host2/scan Note : you can monitor the process Note : Now remove the HDD # echo 1 > /sys/block/sdb/device/delete # fdisk l Note : Now remove the HDD physically
# fdisk l | grep i disk # cd /sys/class/scsi_host/ # ls #cd host2 #ls To Add and remove a ethernet card driver To locate a kernal Modules Step 1 #ethtool i eth0 or Step 2 # cd /lib/modules/ # ls #cd 2.6.32220.el6.x86_64/ #ls #cd kernel/ #cd drivers/
#cd net/ #cd e1000 #ls #modinfo e1000 | more # ethtool i eth0 #lspci | grep i eth /sys/class/net/eth0/device/driver #ls l modprobe r e1000 > To remove a lan card driver Go to console and enter the command #modprobe e1000 # service network restart Now go to putty reload the server To Change the HW address step 1: bring down the interface # ifconfig a # ifconfig eth2 down #ifconfig eth2 hw ether 00:01:02:03:04:05
DU � The Linux “du” (Disk Usage) is a standard Unix/Linux command, used to check the information of disk usage of files and directories on a machine. � The du command also displays the files and directory sizes in a recursively manner. Syntax: du Options -h -s -a -k -m --exclude –time
Descriptions Human Readable Format summary all the files and directories Kilobyte(size in 1024 bytes) Megabytes (MB) exclude any file formats. Ex: du ah exclude="*.txt" /home modification of time Ex: du ha time /home
DD COMMAND � This tool is mainly used for copying and converting data, hence it stands for ‘Data Duplicator’. � Only superuser can execute this command. You should be very careful while using this command as improper usage may cause huge data loss. So, some people consider this tool as ‘Data Destroyer’. � Syntax of ‘dd’ command dd if= of= [Options]
Backing up and restoring an entire hard drive or a partition Description
Command
Backup entire hard drive to another drive.
dd if=/dev/sda of=/dev/sdb bs=4096 conv=noerror,sync
Creating a disk image
dd if=/dev/sda of=/tmp/sdadisk.img
Creating a compressed disk image
dd if=/dev/sda | gzip >/tmp/sdadisk.img.gz
Restoring hard disk image
dd if=/tmp/sdadisk.img of=/dev/sda
Restoring compressed image gzip –dc /tmp/sdadisk.img.gz | dd of=/dev/sda Clone one partition to another
dd if=/dev/sda1 of=/dev/sdb1 bs=4096 conv=noerror,sync
Backing up and Restoring MBR Master Boot record is the boot sector which houses the GRUB boot loader. If MBR got corrupted, we will not be able to boot into Linux. MBR 512 byte data is located at the first sector of the hard disk. It consists of 446 byte bootstrap, 64 byte partition table and 2 bytes signature. Description
Command
Backing up MBR
dd if=/dev/sda of=/tmp/mbr.img bs=512 count=1 The option “count” refers to the number of input blocks to be copied
Backing up the boot data of dd if=/dev/sda of=/tmp/mbr.img bs=446 count=1 MBR excluding the partition table Restoring MBR from MBR image
dd if=/tmp/mbr.img of=/dev/sda
Display master boot record
dd if=/dev/hda of=mbr.bin bs=512 count=1 od xa mbr.bin
Converting data formats Description
Command
Convert the data format of a file from ASCII to EBCDIC
dd if=textfile.ascii of=textfile.ebcdic conv=ebcdic
Convert the data format of a file from EBCDIC to ASCII
dd if=textfile.ebcdic of=textfile.ascii conv=ascii
Converting case of a file Description
Command
Converting a file to Uppercase
dd if=file1 of=file2 conv=ucase
Converting a file to lowercase
dd if=file1 of=file2 conv=lcase
Creating or modifying data files Description
Command
Create a fixed size, say 10MB file
dd if=/dev/zero of=file1 bs=10485760 count=1 The block size is calculated as 10MB=10*1024*1024
Modify the first 512 bytes of a file with null data
dd if=/dev/zero of=file1 bs=512 count=1 conv=notrunc The option ‘notrunc’ refers to do not truncate the file, only replace the first 512 bytes, if it exists. Otherwise, you will get a 512 byte file.
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