Linux

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• C : Computer Management, cat, copy

  • Computer Management

    • $nproc: Displays number of CPU 
    • $free: Displays ram usage
    • $top: Displays disk usage
    • $pf -ef: Displays processes and IDs or $ps -ef | grep "name"`
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  • cat command

    • $cat filename : it will display contents of file.
    • $cat -n filename: it will display contents of file in numbers.
    • $tac filename: it will display contents in reverse order of file.  from bottom to top
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  • copy command

    • $cp source dest	it willl make a copy of the file in the destination.
      $cp -r source dest	it will make a copy of the folder in the destination.
      $cp –rvf /root/* dest	it will copy all files from root folder to dest with confirmation.
      $cp –rvfn /root/* dest	it will copy only new files and not override existing file. v=display, f=forcefully, n=newfiles.

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• D: Date, Daemon, Directory, Delete

  • Date Display

    • Change date & time: run date and copy the line run #date -s “paste and change”.
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  • Daemon: it is a program which control services in the system like services stop start restart reload etc

    • Service Name	Daemon Name
      SSH	SSHD
      HTTP	HTTPD
      NFS	NFS-SERVER
      DNS	NAMED

    • :

    • #systemctl status sshd		Show status of sshd service or systemctl is-active sshd or systemctl is-enabled sshd (enabled means permanently)
      #systemctl stop sshd		To stop sshd service. It is temp stopped until reboot. Systemctl start sshd (restart)
      #systemctl disable sshd		It will stop permanently.  systemctl enable sshd.
      #systemctl reload sshd		Service will reload, it is effective when you make changes. Users will not be disconnected.
      #systemctl restart sshd		Service will restart and all connected users will disconnect.
      Target	4 types you can set	Graphical.target: system state in gui mode multi-user.target,: system state in command line rescue.taget: O/S troubleshooting emergency.target: emergency mode
      #systemctl get-default		To check the system state mode
      #systemctl isolate multi-user.target		It change the system state to command line mode. If you check systemctl get-default it shows graphical.target as it set temp. if system reboot it will start in graphical mode.
      #systemctl Set-default multi-user.target		For permanent set system state into command line mode.
      #Systemctl Poweroff
      #Systemctl Reboot

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  • Delete

    • $rm filename (rm is use to delete file), prompt for confirmation?
    • $rm -f filename (-f = forcefully delete) 
    • $rm -r foldername ( rm -r is use to delete folder)
    • $rm -r -f foldername (forcefully delete folder)
    • $rm -v (verbose, it will display what is going to delete)
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• E: echo, 

  • echo is use to display text message on screen. Generally it is used in script to pass any message on screen.

    • $echo "Welcome "
    • $echo "Welcome to Star Distributors" > welcome.txt (it will save in welcome.txt file, it will create and save, if file exist then it will overwrite)
    • $echo "Online Training in Devops$ >> welcome.txt (it will write next line in welcome.txt)
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• F: File Structure, File/Folder Creation, File Permission, Find, File Size, 

  • File Hierarchy Structure: Files are installed in root (/) directory or root partition. It has 19 subdirectories.

    • / top level root directory.
      /root: it is a home directory for root user.	/bin: contain commands used by normal users.
      /Home: It is a home directory for normal users	/sbin: contain commands used by root user.
      /boot: it contain boot files.	/etc: system configuration files.
      /tmp: stored temporary data.	/dev: disk information is stored.
      /lib 32 & 64: stored libraries.	/opt: contain and stored third party software
      /proc: process information.	/mnt: information about mounting.
      /run: media device which helps to run.

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  • File & Folder create/list/edit,multiple files,

    • #cat > filename	It creates a file and you can enter text. Ctrl D to save.
      #cat >> filename	Add new lines only.  Cannot delete existing lines.
      #cat 2 > filename
      #cat filename	To view/read file.
      #cat –n filename	Displays with line numbers
      #du –sh filename	Displays file size.
      #stat filename	file status and access time.
      #cp source dest	it willl make a copy of the file in the destination.
      #cp -r source dest	it will make a copy of the folder in the destination.
      #cp –rvf /root/* dest	it will copy all files from root folder to dest with confirmation.
      #Cp –rvfn /root/* dest	it will copy only new files and not override existing file. v=display, f=forcefully, n=newfiles.

    • Empty File Creation: touch,
      

      #touch filename location	it creates empty file
      #touch abc{1..10} location	it will create files abc1 to abc10.
      #touch .file1	It will create hidden empty file.

    • Find size of a file: $du -sh filename

    • Edit File: vi or vim,

      vi filename	Create a file in editor. if file exist it open in editor mode. it opens in escape mode, press i to get edit mode to add or delete.
      options	i = insert mode. q! = Exit, wq! Save and exit. x = Delete character where cursor blinking, 4x delete 4char. dw = Delete a word. dd = Delete a line. gg = Cursor goes to top. shift g = Cursor goes to bottom. u = undo. ctrl r = Redo.

    • List files and folders: list,

      #ls	List files and folders of current location.
      #ls -l	Long list
      #ls -a	List all files and folders including hidden.
      #ls -la	Long list of files and folders including hidden.
      #ls -lt	List of files with time stamp, latest created file on the top.
      #ls-R	List directories and all its sub directories.
      #ls-hl	Displays size of the file.
      Ls-lr or ls-ltr	List of files with recently updated. r in reverse order

    • Folder Creation: create, delete,

      #mkdir foldername location	creates folder.
      #mkdir .foldername	creates hidden folder.
      #mkdir –p parent/child	creates parent folder and child folder inside parent folder.
      #rename oldname newname oldname	oldname newname oldname
      #mv sourcefolder dest	It will move folder from source to destination location.
      #mv sourcename destiname	it will copy file in the same location with new name.
      #rm -r foldername	it will delete folder.
      #rm –rvf	delete folder, v= display folder wich will delete, f= forcefully

    
    

    • Multiple commands use with semicolon:
      • $mkdir folder; cd folder; touch file{1..10}
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  • Folder Permission: permission, default permission, 

    • $ls -ld aziz (folder permission): total 11 attributes in folder:
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    • directory	owner	group owner	other	acl(.=no advance permission, +=acl)
      root user default d	rwx	r-x	r-x	.
      normal user   d	rwx	rwx	r-x

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  • File Permission: 

    • ls -l : Displays file & folder permissions
    • ls -l filename : Displays particular file permissions

    • file	owner	group	other	no acl
      root user	rw-	r--	r--	.
      normal user	rw-	rw-	r--

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  • Assign File and folder permission with numeric Method: Attributes : Read (r=4), Write (w=2), Execute(x=1), chmod

    • no permission=0Execute permission oly = 1

      write permission  only =2

      write and execute permission =3(2+1)

      read permision only = 4

      Read and execute permission= 5(4+1)

      read and write permission = 6 (4+2)

      read,write & execute permission = 7 (4+2+1)

       #Ls –ld /folder1 (drwx r-x r-x. 2 root root 10 sep 13:35 /folder1), assign full permission to group.

      #chmod 775 folder1 (drwx rwx r-x. 2 root root 10 sep 13:35 /folder1

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  • Assign file and folder permissions with Symbolic Method:chmod

    • Ls –ld /folder1 (drwx r-x r-x. 2 root root 10 sep 13:35 /folder1), Remove read permission on folder1 for others: 
    • chmod o-r /folder1 , drwx r-x --x. 2 root root 10 sep 13:35 /folder1 (chmod = change file mod bits)
    • Adding read permission on folder1 for other:
      • chmod o+r /folder1
    • Set permission to a folder:
      • chmod o=rwx or o=rw or o=r-- /folder2
      • chmod o=--- /folder2 (other user cannot do any thing)
    • Assign permission to only user1 and rest denied.

      • Method1: Add user1 to group and assign permission to group.

        Usermod –G root user1 (groups user1: will display groups of user1)

        Method2: groupadd dev

        Chgrp dev /folder2 (ls –ld /folder2/) now group owner from root changed to dev.

        Add a user to group dev (usermod –G dev user1)

        Add user1 as owner of the folder2

        chown user1 /folder2

        Change both owner and group owner

        chown root:root /folder2 (root will be the owner of folder and group) (chown=change file owner and group)

        you can do this way:  chmod u=---, g=---,o=--- /folder2 or chmod ugo=rwx /folder2 or chmod ugo-x /folder2 or chmod +x /folder2 or chmod –x /folder2.

    • ACL: access control list
  • Find: 

    • Syntax: $find location options argument
      $find / -name aziz	it will find aziz from / root location.
      $find / -readable	it will find readable permission files from root location
      $find /root empty	it will find empty files in /root directory.
      $find / -perm 444	find files whose permission is 444
      $find / -size 10M	find files whose size is 10M
      $du -sh filename	Find size of the file

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• G : Grep, 

  • grep option argument filename: 

    • 	$grep root /etc/passwd	It will find/search root word in passwd file and display those lines on screen.
      option -n	$grep -n root /etc/passwd	It will search and display the line numbers on which root word exist.
      option -i	$grep –ni Root /etc/passwd	Ignore case sensitive (word with upper or lower case will be ignored)
      option -on	$grep -o root /etc/passwd	It will only display word in the line, will not display the entire line.
      option '^word'	$grep '^root' /etc/passwd	It will only display line where word root comes at the beginning of line.
      option -A number	$grep -A 2 root /etc/passwd	it will display root line and 2 lines after word root from file.
      option -B number	$grep -B 2 root /etc/passwd	it will display root line and 2 lines before word root from file.
      	$egrep –in ‘root|ftp|nologon’ /etc/passwd	Used for multiple words to search.
      option -R	$grep -Rin root /etc	it will seach the entire folder for work root.
      	$grep –in ‘Sep’ /var/log/messages	It will display logs of Sep
      	$grep –in ‘Sep 05’ /var/…	It will display logs of sept 5

       

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• H : Help, Head/Tail, 

  • Help Command:

    • command --help or man command: both commands can be use to get help.
      • cat --help
      • man cat: it uses to display manual or help of any command.  man cd (displays manual of cd command)
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  • Head command: it is used to read file, head command displays only top 10 lines of a file while cat command displays the entire file.

    • head abd.txt
    • head abd.txt | nl (displays with number)
    • head abd.txt | cat –n (head abd.txt –n 15 | cat –n (it displays 15 lines))
  • Tail command: tail is used to display bottom to top lines

    • Tail –F /var/log/messages (it will run file continuously without closing and keep displaying a new lines added to logfile) while cat file will display text and any new lines updated will not display.
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• I: Installation of Ubuntu, RHEL, Centos

  • Installation RHEL on VMWare Workstation

    • Download ISO image (search in google: rhel 7 image download)
    • open vmware and create a new vm
    • Enter vm name, location of ISO, RAM, disk size etc..and poweron
      • select Date & time, keyboard, Language support
      • select installation source: local or network
      • Software selection: minimal, infrastructure server, file and print server, basic web server, virtualization host, Server with GUI,
      • Installation destination: select disk and click I will configure partitioning and click done --> select standard partition and click + and define following partition type
        • select / : Root partition: min 3 GB add mount point.
        • / boot :Boot Partition: 500 MB size define add mount point.
        • Swap partition: 2 GB size define and add mount point.
        • Add a disk: adding additional disk.
      • Network & Hostname:
        • Network: configure and enter IP address manually or through DHCP.
        • Hostname: enter hostname, click begin installation
        • root password:enter root password, create a normal user and click done, installation begins which last for 30 to 40 min.  After completion reboot.
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  • Installation of Ubuntu

    • Download ISO image ubuntu-22.04.3-desktop-amd64.iso
    • In vmware workstation, create new VM, install O/S later, linux = ubuntu 64 bit, save and edit the VM and define location of ISO, network adapter=bridged. power on VM.
    • select try or install ubunut, select install ubuntu, normal installation with updates and continue, enter name other than admin, password, login autimatically and continue.
    • open terminal abdul@ubuntu-tomcat:/$ sudo apt update
    • abdul@ubuntu-tomcat:/$ java (if java is not installed then it will give commands and versions to install. copy and run.
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  • Installing package: ex java 

    • Before installing any package, first update apt respository $sudo apt update or $sudo apt-get update (earlier apt-get used)
    • $sudo apt-get install (/etc/apt/sources.list = the lists of available packages) or search $apt-cache search jdk  
      • when you try to install any package it search in apt repository, if it is not available it gives en error and need to download the package.
      • $java (it displays the  version of java installed or provide information how to install), headless = there is no GUI.
    • Installation docker with script:
      • Any package wich is not availabel in apt repository, which required to download and then install, it can have multiple commands to run, instead of running each command, can included all in script and run.
      • Method 1:
      • step 1: setup docker's apt repository:

        • sudo apt-get update
          sudo apt-get install ca-certificates curl
          sudo install -m 0755 -d /etc/apt/keyrings
          sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
          sudo chmod a+r /etc/apt/keyrings/docker.asc

      • Step 2: Install docker
        • sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
      • Step 3 : Verify
        • sudo docker run hello-world
      • Method 2:
        • #vi docker_install.sh
        • paste all the commands of step 1 & step 2 save and exit
        • $ chmod +x docker_install.sh (assign permission to run the file or executable)
        • $./docker_install.sh (run the script)
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• J : Job Sceduling, 

  • Job Scheduling: Crontab

    • at		It is used to schedule a job only once.  Make sure at job available in the system, rpm –qa | grep –I at, its daemon is atd.
      	at 12:50 at> touch abc at>touch file1 ctrl D	At 12:50 time it schedule a job and creates two files abc & file1 or you can define particular time and date. at 12:00 PM October 20  2020 or at noon tomorrow, at next Monday, at fri
      atrm	atrm 4	Remove job with job number
      atq		Displays scheduled job list
      crontab		It is used to schedule job continuously or repeatedly.
      	rpm -qa | grep crontab	To check crontab module is installed. yum install crontab. Systemctl start crond.
      Syntax	Cat /etc/crontab	It will display syntax. (Min, hour, day, month, day of week, username, command)
      	crontab -e	It opens an editor, here you write command using above syntax 39     09      01    jan   03   root    echo “welcome” >> test.txt  save it.     If you use * in minute then it will run every minute.  If you use */2 run every 2 minutes.
      	crontab -l	It displays list of scheduled jobs
      	watch  cat test.txt	It will open a file and we have define job schedule in every minute.
      	crontab -r	Delete.
      	Crontab -u username -e	Run crontab with a particular username.
      	Tail -f /var/log/cron	Check logs.
      	Crontab -r -I -u username filename
      	Sleep 60
      	Cd /etc/cron.hourly	Here you keep script, this file normally used in day to daty scheduling jobs in real time scenario instead of crontab,

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• K: Kernel, 

  • Kernel

    • Kernel is a O/S program which makes communication between application (chrome, facebook, etc..) and hardware.
    • Applications do not communicate directly with hardware, o/s kernel make it possible.
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• L: List, 

  • List commands

    • ls = display list of files and folders
    • ls -a =  display list with hidden files.
    • $ls -l = Displays list of files & folders with file permissions
    • ls -ltr = display list with directory or file, permission, user, group, size, timestamp.
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• M

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• N: Networking

  • Networking: 

    • $ifconfig: displays LAN settings.
    • $nmtui: define ip address
    • $nmcli:
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• P: Ping, Print, Password, Partition Management, pipe, 

  • Print Message / echo: It will print message on screen only.

    • #echo “message”	It will print message on screen only.
      #echo “message” > filename	It will store message in a file.

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  • Password: Break Root Password: if root user password is forgotten, then

    • restart the system and continuously press up and down arrow key and system will not reboot and halt at o/s selection screen. Select the first line and press ‘e’ to edit. 
    • Go down until reach linux16 line and come to end the line (press keyboard End key or Ctrl E)
    • give space and write rd.break (break ram disk) ctrl X to start. It will on in rescue mode. 
    • Run this command mount –o remount rw /sysroot and enter.
    • chroot /root and enter.
    • passwd root and enter (it will edit /etc/shadow file).  set new password. 
    • Create a file touch /.autorelabel and type exit enter and again exit enter.
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  • Partition Management: 

    • Hard disk types: SATA (Serial Attach) and PATA(Parallel Attach)

                              SATA (disks: sda, sdb, sdc,… partitions sda1, sda2, sda3.. sdb1, sdb2, sdb3..)

                              PATA (disks: hda, hdb, hdc,.. partitions: hda1, hda2, hda3.. hdb1, hdb2, hdb3)

      Maximum partitions : 4 (4 primary only) or (3 primary + Extended (in extended logical No.n)

      Format : ext2 (RHEL4), ext3(RHEL5), ext4(RHEL6) xfs (RHEL7)

    •  Disk Partition: 

      Disk & partition	fdisk–l	Display disks & partitions.
      	lsblk	Display disks & partitions in a tree format.
      	lsblk –l	Display disks & partitions in list format.
      Create partition	fdisk /dev/sdb	In order to create partitions first you need to enter into disk, all disk info is stored in /dev. Enter m will give list to perform actions.
      Update kernel	partprobe	After creating a new partition or making any changes in partition kernel need to update with partprobe command.  If you try to format without partprobe system will give error partition does not exist.  Reboot the system will update kernel without using partprobe.
      	partprobe /dev/sdb	It will update particular hard disk. Partbrobe only will update kernel for all disks.
      Format partition	blkid	To check partition is formatted or not.  Data can be saved after formatting the newly created partitions. If partitions are not shown in the list it means it is not formatted. After formatting you can save data.
      	Mkfs –t ext2 /dev/sdb1	It will format the partition.  Ext1, Ext2, Ext3,Ext4, XFS is the file system.
      Create a directory/file to mount	Mkdir /dev/sdb1/partition1	First create a directory and then mount this directory and then you can save data.
      Mount partition	Mount /dev/sdb1 /partition1	After creating new partition, partprobe, format need to mount the partition to save the data. After mounting you can save data.
      Display mount partitions	Df –h	It will display all partitions that are mounted.
      Unmount partition	Umount /partition1	When you reboot this mount will not exist.
      Mount permanently	Vim /etc/fstab	To mount partition permanently even it exist after reboot.
      	Make an entry	/dev/sdb1  /partition1 ext2   defaults 0 0  save it.
      	Mount –a	This will update entries made in fstab.
      Format	Mkfs –t ext3 /dev/sdb2	It will format sdb2 partition. Copy UUID
      Mount with UUID	Mkdir /partition2	Go to vim /etc/fstab and make entry with UUID. UUID=”jldfjawje” /partition2  ext3  defaults 0 0
      	Mount –a
      Vfat		If you partition with vfat then it will work with windows system while ext will not.
      	Mkfs –t vfat /dev/sdb5	Make partition and mount.
      	Mkfs –t xfs /dev/sdb6	Partition using xfs, make folder and mount.
      Unmount	Umount /partition1	Go to fstab and delete those lines. Save & mount –a. now go to fdisk –l and delete partitions. Partprobe /dev/sdb

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  • Swap Partition / temp memory / virtual memory: 

    • All runtime processes need space to process and it takes RAM, when RAM is getting full then processes cannot be executed and system get hanged, to overcome this situation we create a partition and assign swap file system.  It gets linked with physical RAM and to run process if it required space then older processes shifted to swap memory and new process is dealt by RAM.
    • Max 64 GB can be swap only.  Swap partition hexcode (ID) is 82.  So assign hexcode to this partition. Press t then 1.

    • Swap partition	Free -h	It will display swap partition details.
      	Swapon -s
      		Add hard disk for swap memory and reboot/ partition create.
      	Mkswap /dev/sdb1	Create a swap
      	Swapon sdb1	It will activate.when reboot it will disappear.
      Mount	Vim /etc/fstab	Entry: dev/sdb1   swap    swap   defaults 0 0 save it and run mount -a
      Deactivate	Swapoff /dev/sdb1	Go to fstab and remove entry and run mount -a and remove partition if needed.  Partprobe /dev/sdb
      Swap partition through file, if partition limit is full then you can use a space in the hard disk and create a file and this file use as swap partition.
      Create	dd if=dev/zero of=/swapfile bs=512mb count=2	Create a file take a space from hard disk and create a file at root level. Block size will be 512 mb and count two times means will create 1024 mb or 1GB.
      	du -sh	It will display size of the created file.
      	mkswap /swapfile	Create a swap.
      	swapon /swapfile	Activate it.  Give permission 600(chmod 600 /swapfile)
      	Vim /etc/fstab	Entry: /swapfile swap swap defaults 0 0 save it then run mount -a
      Deactivate	Swapoff /swapfile
      	Rm -rf /swapfile	Delete file.

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  • Pipe | is use to run the command by using the result of first command.

    • $cat filename | nl (it will display the contents of file in first command and after pipe it will display in number list)
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  • Ping install on docker containers

    • $apt install -y iputils-ping
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• Q

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• R: Rename

  • Rename file and folder

    • $rename oldname newname oldname
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• S: Sudo, Software Management, Shutdown/Reboot, SSH

  • Shutdown / Reboot : 

    • Systemctl	Reboot (alias of systemctl)	Gracefully reboot system
      	Init 6	Forecefully reboot
      reboot	Shutdown –r 15:50	Reboot at 15:50
      	Shutdown - +15	Reboot after 15 min
      	Shutdown –r now	Reboot now
      	Shutdown –c	Cancel reboot.
      	Shutdown –r now	Reboot now
      Shutdown	Shutdown –h now	It will shutdown now.

       

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  • Software Management:

    • #rpm –qa		It will display all packages installed.
      #rpm –qa | wc –l		Total number of packages installed.
      #rpm –qa firefox		It will display firefox is installed or not.
      #firefox		Browser will open or can be opened from application
      #rpm –ev firefox		E is for erase and v for verbose (you can view the process)
      Install firefox	On VMWare with GUI	vmware settings: select vm>settings>use ISO image and browse location of image.  click on cd/dvd icon in bottom and connect. CD icon appears on desktop. Go to RHEL folder in CD>package> search firefox, copy package and paste on desktop and install.
      	Install with RPM #rpm –ivh firefox…….	#df –h (To check CD iss mounted), cd /run/media/root/RHEL7.0/serverx86 and cd/Packages, #ls #rpm –ivh firefox….. press tab and install.
      	#rpm –Uvh firefox	It will install update
      	#rpm –ivh forefox –force	Forcefully it install
      YUM		It is used to install packages in Centos.
      	Yum list all	It shows all packages
      	Yum repolist	It list repository
      	Yum list installed	It list those package who are installed
      	Yum list httpd
      	Yum list nfs-utils
      	Yum info httpd
      	Yum reinstall httpd
      	Yum update httpd
      	Yum remove httpd	Yum autoremove httpd (it will remove dependencies)
      	Hum history
      	Yum history info 4	It shows details of ID 4 installed
      	Yum history undo 4	It will undo the ID 4 (uninstall)
      Logs	cd /var/log	Tail –F yum.log
      	Yum search all “web server”	It shows webs server package
      	Yum search all “mail server”	It shows mail server package
      	Yum search all “dns server”	It shows dns server package
      	Repository	Local and network.
      create	Local repository	Create a folder mkdir /examplerpm Copy data from CD to /examplerpm (all files from CD incl repodata copied). cd /etc/yum.repo.d vim /example/repo   [example] name  =file:///examplerpm enabled = 1 gpgcheck = 0 save this file run yum clean all yum repo list (when you run yum command it will search in this file) all rpm files are in Package folder and how does system knows?  It will look repodata and if found then proceed installation.  repodata will inform where is rpm files are stored.
      create	repodata	Mkdir/software/itrpm (create folders) Createrep /software/ cd /etc/yum.repo.d vim itrpm.repo baseurl =file:///software enabled = 1 gpgcheck = 0 save it
      	yum repolist	It will list repo files created.
      Amend	update repodata	If you add/delete any rpm then repodata need to be update. Createrepo --update /software/
      Network Repository		Repodata created in network server.

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  • Sudo: Super User DO #

    •  It allows a user to execute a command as a super user. By default superuser(root) have got all administrative privilege but it is mostly locked and we create normal user and assigned required roles or permission to perform their task. You can run command with administrative privilege by using sudo.

    • To switch user to root = sudo su , swith to user = su username

    •  

      $sudo fdisk –l (it will ask password to confirm user, if this user is in sudo file then it works)

      To give access to a user to run such commands first get the command binary

      #which fdisk –l (it will display binary of the command)

      Go to sudoers file by vim /etc/sudoers

      se –nu (it will display line numbers) go to line 100 and press o to insert a line.

      username   ALL=(ALL)   ALL     (this user can run all commands which root can)

      if you want a user to give permission to a particular command then instead of all type

      username   ALL=(ALL)    /sbin/fdisk, /sbin/useradd   save it.

      If you want to give full permission except few restriction then

      Username ALL=(ALL)    ALL,!/sbin/reboot, !/sbin/useradd, !/usr/bin/passwd (now user cannot reboot, cannot create user and assign password)  save it.

      To assign similar permission to another user, copy the line & paste and change username.  The best example is create a group and assign permission to that group and add required users to that group.

      groupadd security (created a security group).

      Gpasswd –M user1,user2,user3 security  (to check user added run grep security etc/group)

      Now go to vim /etc/sudoers and add group

      %security   ALL=(ALL)    ALL

      When a user run command using sudo system ask for password, you can skip this by

      Username   ALL=(ALL)     NOPASSWD:ALL  save it.

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  • SSH:

    • $sudo apt install openssh-server
    • $sudo apt install openssh-client
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• T: Terminal

  • Terminal:

    • Alt+F2 type Gnome-terminal	It will open a terminal.
      ctrl+D	Close terminal
      Alt&shift+++	It will increase font size.
      Alt&---	It will decrease font size
      Alt+F10	Window full size
      Alt+F5	Window normal size.

       

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• U: User management, usefull commands 

  • User Management:

    • root@hostname:~#	root = user name, @ hostname(hostname or IP), ~ (tild sysmbol shows you are in home directory of root user, when you change directory it shows directory name), # denotes you are root user.
      aziz@hostname:~$	aziz =user name, @hostname,(hostname or IP) ~ is the user home directory, $ denotes normal user, Normal User UID = 1000 to 60000 GID 1000 to 60000 (this range can be increased in /etc/login.defs).
      System User	DNS, DHCP, FTP, Apache, Samba, NFS etc.. used to manage services, 1 to 999 GID (1to999) in RHEL7, in RHEL6 UID =1to 499 & GID=1 to 499.
      UID (user ID) and GID (Group ID) is assigned to a user and all policies are assigned to that ID.
      #cat /etc/passwd user information stored in this path.	root:x:0:0:root:/root:/bin/bash root = user’s login name x = password pointer /etc/shadow, password is set (! = password is not set): 0 =UID 0 = GID root = comments (define designation of user, administrator, manager etc..) root = user’s home directory /bin/bash = login shell
      # /etc/shadow Password information is stored in this path.	root: xfaddoiuabelrje :  : : : : : : (9 fields) root = username X39u3lkaefj = password in encrypted format 3 to 9 fileds=  stored user password policies.
      #/etc/group Group information is stored in this path.	root:x:0: ziz, Abdul, user1, user2 root = group name x = password pointer (/etc/gshadow) password set 0=GID Aziz,Abdul,user1.. = group members.
      #/etc/gshadow Group password stored in this path.	Root: aoplw2lj fl : aziz : user1, user 2 (4 field) Root = Group name Alskjfoweivnl = encrypted password 0 = GID Aziz = Group Admin user1,user2 … = list of members.
      #/var/mail/root	Mail information is stored in this path.

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  • Create user/group: Syntax = adduser/addgroup option argu username/groupname

    • #adduser ali (user ali will be created and prompt to enter details like, password, full name, roomnumber, work phone etc..) or useradd can also be used where user will be created wihout details.
    • when a user is created a group with same name is also created. 
      • with comment: $useradd –c “Receptionist” saif ( -c used to comment)
      • with ID: useradd –u 1010 adnan (user ID is manually entered)
      • with Home Directory: useradd –d /userdata/haroon haroon (create a folder userdata, user haroon home directory is created in userdata folder).
      • if you want to change user home directory to custom directory for all users, then change the file, vim etc/default/useradd
      • Hidden files: when you create a user, in its home directory there are some hidden files created.          .    ..    .bash_logout   .bash_profile    .bashrc     .mozilla  (if these files are corrupt or deleted, then user will not get shell (prompt), to recover these files are stored in central location and from there it is copied to /home folder), copy these files /etc/skel and check these files, copied and paste in /home folder. (cp -rvf .bash_logout …… .mozilla /home/user2)
      • There are some files/folders which should be copied to user home directory by default when a user is created.  Go to vim /etc/default/useradd and append skel=(give folder name whose files/folders need to be copied).  Create a user and you login with this user which will not have shell but data will be copied, /etc/skel here all profile data is saved and we append this location.  The best solution is copy all data into /etc/skel and create a user which allow user to login and data will also be copied in their home directory.
      • /bin/bash : it allows user to login.
      • useradd –s /bin/nologin mohamoud (it wont allow to login)code
  • Delete a user:

    • Check a user home directory by going to cd /home , #ls -ll(long list)
    • #Userdel ali (user ali account will be deleted but home directory exist)
    • #Userdel –rf username or #userdel --remove-home username (user saif is deleted along with home directory)
  • User modification: 

    • User creation with password assigned: without password user cannot login.  Root user can switch to any user even the user has password has not been assigned.

      useradd user1 (user created without password)

      passwd user 1 (system prompt to assign password)

      user to user switch: user can switch another user by assigning password, exit to come out.

      user to root switch: user cannot switch to root user.

      Check password assigned? Passwd -S user1 (S = status).

      Password Lock : passwd -l user1 (password locked, user to user switch login denied, root user can login), passwd -S user1 (check password status)

      unlock password: passwd -u user1 (password unlocked)

      passwd -S user1 (check password status)

      password delete: passwd -d user1( user password deleted)

      passwd -S user1 (Password status check)

      user creation using script and assigned a password:

      vim usercreation.sh (press i to go to insert mode)

      #! /bin/bash

      useradd user10

      echo India123| passwd - -stdin user10 (press esc)

      :wq! (save script)

      RUN SCRIPT

      sh usercreation.sh (user created with password assigned)

      passwd -S user10 (check password status)

      User Account Policies:

      Chage -l user1 (shows account aging information)

      Chage user1 (to reset the account options)

      To change a particular record, chage -option newvalue username (chage - -help check)

    • add additional group to user: suppose a user run #docker pull hello-world (only root have permission), add user to docker group.
      • #usermod username -aG docker
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  • usefull commands related with users:

    • #cat /etc/passwd (all list of users with user details)
    • #head /etc/passwd (list top 5 users)
    • #tail /etc/passwd (list last 5 users)
    • #grep aziz /etc/passwd (user aziz information)
    • #cat /etc/shadow (password details )
    • #grep aziz /etc/shadow (aziz password information)
    • #cat /etc/group (list and details of group)
    • #grep groupname /etc/group (users of group)
    • #cat /etc/gshadow
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• W

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• X

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• Y

  • yum command : yum

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• Z: Zip/Unzip, 

  • Zip/Unzip:

    • Compressed file: tar is used to archive files, for compression use gunzip, bunzip or xz commands.
    • Archiving:

      • tar options archivefoldername file&folder, create a folder and go to folder and run

      • tar –cvf redhad.tar /etc (c for create, v for verbose, f for file type) it start archiving.

      • du –sh redhad.tar (display size = 30 mb, before archive it was 34 mb)

      • tar –xvf redhad.tar (it extract files in the same location and display contents of tar file)

      • tar –xvf redhad.tar –C /tmp/ (it will extract in tmp folder)

      • tar –tvf redhad.tar (list files)

    • Compress:

      • tar –zvf redhat.gz /etc (it will compress etc folder as rehat.gz)

        tar –zcvf rehat.tar.gz /etc (it will archive and compress)

        du –sh redhat.tar redhat.gz (30 mb redhat.tar and 8.4mb redhat.tar.gz)

        tar –jcvf redhat.tar.bz2 /etc (using gunzip command to archive and compress)

        du –sh redhat.tar redhat.tar.gz redhat.tar.bz2 (30 mb, 8.4 mb,  7.0 mb)

        tar –Jcvf redhat.tar.xz /etc (using xz command, J is capital)

        du –sh redhat.tar.xz (5.7 mb)

    • Extract:

      • tar –zxvf redhat.tar.gz (It will extract, use x instead of c)

      • tar –jxvf redhat.tar.bz2

      • tar –Jxvf redhat.tar.xz

  • Check zip in installed:

    • Zip: to check zip is installed (rpm –qa  zip) (rpm –qa unzip)

    • zip abc.zip /etc (it will zip etc folder in abc.zip)

    • du –sh abc.zip (size 4.0k)

    • unzip abc.zip (it will unzip)

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