* $ mkdir folder-name{1..50} # {} encloses a range and creates 50 folder in linux
* $ useradd user-name # Creates a new user
* $ pinky # shows information of all available users
* $ rm -f # Forcefully remove files
* $ rm -fv # forcefully remove file with an action responding work done
* press F2 # used to rename a file
* $ cal September 1752 # shows september calendar with dates missing from 3 to 13
* $ date +%Y # Current year
* $ date +%A # Current Weekday
* $ date +%T # Current Time
* $ date --help # all options available with date command
* $ cal -j # Shows Julean Calendar
* $ bc # opens a calculator
* $ ls -F # check which is folder and which is file in a directory
* $ mkdir -p folder1/folder2 # both folders will be created together
* $ rm -rf pi* # deletes all folders starting with 'pi' , use anything instead of 'pi'
* $ su # switch users through command line
* $ uname #name of the kernel used in OS
* $ uname -r # version of the currently used kernel
* $ strace date # S stand for system, it shows the background functioning of command (system call)
* $ shell-name # it changes the shell currently being used, and to close just type exit
* $ cat # it is file viewer
* $ uptime # Details about time since when last logined
* $ !history-number # history-number represents the sequence number of command in history and it runs the command again
* $ !starting-text-of-command(bottom-up approach) #same as above
* $ echo variable-name # if variable is not existing , it gives blank without error
* $ echo $ SHELL # predefined variable to show shell name
* $ echo $ USER # predefined variable to show logged in user
* $ echo $ LANG # shows default system language
* $ echo $ HISTSIZE # no of history commands that can be saved
* $ echo $ HISTFILE # storage location of history file
* $ PSI="Pykid : -- > " # inside " " anything can be written and it will be seen as written in terminal left side
* $ env # shows all primitive/predefined commands
* $ alias variable-name='command' # used to create alias / alternative of any command
* $ source path-of-file # it merges any new changes made outside of terminal
* $ tput bold # change text inside Terminal to bold
* $ tput setab 3 # changes background color of terminal
* $ script -t 2>script-name.txt # stores all actions performed in a script file
* $ scriptreplay script-name # replays all commands made on terminal
* $ which and $ whereis # shows tthe stored path for any software or file
* $ echo $PATH # gives the path of various directories where primitive commands are stored
(Director1 : Directory2 : DirectoryN)
* $ wc -l file-name.extension # count no. of line in file
* $ wc -w file-name.extension # count no. of words in file
* $ wc -c file-name.extension # count no. of characters in file
* $ grep search-text where-to-search # finds the text with similar pattern
* $ grep -i search-text where-to-search # finds the text (Non-Case Sensitive)
* $ grep -w search-text where-to-search # find the text with exact word
* $ grep -v search-text where-to-search # find the text that doesn't match the search-text
* $ head -n file-name # extracts n lines from top of file
* $ tail -n file-name # extracts n lines from bottom of file
* $ `command`file-name.txt # back quotes make command work if no space is given
* $ tar -cvf new-file.tar file-name.extension # c - create ; v - visual ; f - forcefully , creates a archive
* $ ls -lh # shows file size in respective formats (kb/mb/gb)
* $ ls -l # shows file info ( size, permissions, name) , size in kb
* $ tar -tvf new-file.tar file-name.extension # shows the files present in archive
* $ tar -xvf new-file.tar # extracts all files out of tar/archive
* $ tar -czvf new.tar.gz file1.ext file2.ext # z- gzip , it commpreses the large files into size of Kbs
* $ chmod 400 file-name.extension # Secures the file from public
* $ ssh user-name@IP # To connect to IP of different instance
* $ ssh -i key-path user-name@IP # red hat command to connect to cloud instance
* $ sudo -i # switch user to root without password when connected to cloud instance
* $ passwd user-name # give password to a user
* $ userdel -r user-name # removes user, -r removes all data stored by user being removed
* $ adduser user-name # add user in ubuntu OS
* $ id -u # shows the id of user
* $ lpr file-name # used to print files
* $ ls -ld # shows inode table of directory itself
* $ ls -ild # shows inode number of directory
* $ ls -l # shows inode table of files inside a directory
* $ chgrp grp-name # create a group
* $ chgrp grp-name directory-path # changes creators name to group name
* $ chown owner-name new-name # change owner name
* $ useradd -G grp-name user-name # add a user to existing group
* $ usermod grp-name user-name # add a user to existing group if user already exists
* lsblk # shows partitions and hard disks in red Redhat
* fdisk -l # shows partitions in present hard-disk
* $ setfacl -b file.ext # Remove all ACL permissions
* $ setfacl -x u:user-name file.ext # Remove single user ACL
* $ yum provides package-name # it tells us which repo provides the specific package
* $ yum reinstall package-name #reinstalls the specified package
* $ fdisk -l # no of hdd attached to linux
* $ fdisk -l disk-name # shows only the hdd with disk-name given
* fdisk disk-name # enter in the disk
* mkfs.xfs partition-name # mkfs - > make file system , xfs - > supportable format
* $ df # disk free , shows the path of new partition or HDD mounted on OS
* $ df -h # path of new partitions in human readable format
* $ df -hT # shows format type
* $ rpm -q package-name # package available to in system
* $ rpm -qc package-name # query configuration
* $ systemctl start package-name # start the service of your package
* $ systemctl status package-name # check the status of your services
* $ tac file-name.txt # reverse the order of reading from bottom to top
* $ rev file-name.txt # reverse the words in file reading from top to bottom
* $ qrencode -s 16x16 -o file-name.png web-site-link # Creates a QR code for the websites, -o shows output to save
* $ systemctl enable docker # start the docker each time OS
* $ systemctl start docker # initiate docker
* $ docker ps # shows running iso file
* $ docker ps -a # shows all containers running or shut-down
* $ docker ps -qa # shows all id's of all pre-made containers
* $ docker rm $(docker ps -qa) # delete all the containers
* $ docker tag old-iso-name new-iso-name # make a copy of old-iso image with a new name with same id
* $ docker rmi docker-image-tag # removes the docker image with tag provided
* $ docker inspect elated_yonath # gives details about docker from which we can get ip
* $ kill -s STOP 'pidof firefox' # used to send a process of firefoox in pause state
* $ kill -s CONT 'pidof firefox' # it will resume the state of firefoox
* $ docker run -itd docker-image process -name # d - > dettach, run the container but user doesn't login to container instead container moves to background
* $ docker stop container-id # to stop a running containers
* To clear cache memory of system run command
sync; echo 3 | sudo tee /proc/sys/vm/drop_caches
* $ mount -o remount,rw / # if opens read only mode in emergency mode
* $ dhclient -r # to remove previous dhcp state
* $ dhclient -v br0 # to restart dhcp client and provide with dhcp service to local system
* $ nmtui # it opens network ip allocation GUI- fdisk -l # to check your attached volume are attached properly
- Create virtual HDD by
- creating a physical volume by run the Command
$ pvcreate disk-name-1 disk-name-2
- run Command - provides a name to virtual group
$ vgcreate virtual-hard-disk-name /dev/hdd-name1 /dev/hdd-name2..
- to display the created hdd , run Command
$ vgdisplay virtual-hdd-name
- finally create a LVM
$ lvcreate --name lv-name --size size-name virt-hdd-name
- to check final virtual group status run
$ lvdisplay
- now you can create partition and use HDD
- LVM stands for Logical Volume Manager
- -l extents - > it is used to provide size in terms of extents
lvcreate --name tech -l 30 vg-name
- to display the content of lvm in short use
lvs - to give a physical extent size to vg group usw
-s
vgcreate -s 16M vg-name hdd-name1 hdd-name2
- It works on thin provision
- It allocates memory on run time
2**24filesystem can be created from single Pool- it formats the filesystem as well
- dm-raid - > handles the system output in terms of storage
- maximum size of Pool can be only 1 terabyte
- Block-Devices refers to the hard disk
- By default it works over xfs only
- it requires package
stratisd and stratis-cli - to get local repo for rhel8
baseurl=ftp://192.168.10.254/pub/rhel8/AppStream/
baseurl=ftp://192.168.10.254/pub/rhel8/BaseOS/
- start its services by
systemctl start stratisd.service
systemctl enable stratisd.service
- to create a Pool
stratis pool create pool-name Block-device-name1 block-device-name2
- to check Pool
stratis pool list
- to check block devices attached
stratis blockdev list
- to create filesystem
stratis filesystem create name-of-pool-to-use filesystem-name1
- to mount you can use Device name1
mount /stratis/pool-name/file-name /mnt/folder-name1
- to extend pool storage / or attach another HDD
stratis pool add-data pool-name disk-name
- its fstab should be written as such that first stratis service should be up then only mount the device
device-path mount-folder-path format defaults,x-systemd.requires=stratisd.service 0 0
-
in format 0 0 defines backup and protection by company default structure
-
To create a snapshot(backup) of filesystem
stratis filesystem snapshot pool-name filesystem-name-to-make-snapshot-of file-name-of-snapshot
stratis filesystem snapshot pool1 file1 snap1
- to find the created list of snapshots
stratis filesystem list
- a snapshot is a copy of file system which can be allocated anywhere and it takes size from pool (maybe not sure)
- for ubuntu ( sudo apt-get install kernel-nfs-server)
- for rhel ( sudo yum install nfs-utils )
- Create a directory to use as nfs ( mkdir /shareable-directory)
vi /etc/exportsdirectory-path ip-to-allow-to-connect(rw or ro,no_root_squash)exportfs -r# it makes all files shareable on server, basically reloads the exports filechmod 757 directory-path- showmount -e ip-of-server ( All traffic should be open )
-
showmount -e server-ip
-
mount server-ip:directory-path directory-path-to-mount-on
-
entry in fstab
source-ip:directory-path where-to-mount nfs _netdev 0 0 -
ifconfig
br0: -
ifnet is the private ip
-
lancard of ethernet is eno1
-
lancard of wifi is wl
-
bridgecard is br0
-
in exam many things are configured on br0
-
Fixing an IP is termed as static ip
- ping ip-address -> find a ip which shows Destination Host Unreachable
- ping server-name (if not possible then set in resolv.conf )
- set ip not reachable
cd /etc/sysconfig/network-scripts/
- name of file in this directory should be ifcfg-lan_card_name
example ifcfg-eth0
- vi ifcfg-etho
- change BOOTPROTO="static"
- NAME = "lan-card-name"
- ONBOOT = "yes"
- in last line
IPADDR= 192.168.10.43 DNS=192.168.10.254 (server will be given,name-server/domain-name-server) NETMASK= 255.255.255.0 - > single public ip (can be taken from ifconfig) GATEWAY= 192.168.10.1 (ip to communicates with outside world)- route -n # shows the values of kernel ip routing table
- 0.0.0.0 means anywhere
- run command
systemctl restart network-online.target- after configuration, reboot which must show the set ip
- resolv.conf - > gives ip from name
- after setting static ip
- open
/etc/resolv.conf - nameserver ip-address-of-eth0
- NTP is configured for security purpose
- The time of server and local machine should be similar to be able to work upon somekind of network
- it is used by package called
chrony - in conf file of chrony
/etc/chrony.conf, enter
server adhocnw.example.com
- restart service
systemctl restart chronyd
- enable the service
systemctl enable chronyd
- to check the server information
chronyc sourcestats
- offset -> in how much time it synchronises the time with server
- to get complete info
chronyc tracking
- official website of ntp : www.pool.ntp.org
- hard-disk can be used as a RAM
- swap memory - > using the hard-disk partition as a RAM
- to check swap
free -m - RAM 2G - > SWAP 2G
- RAM 8G -> SWAP 4G
* make partition
* mkswap hdd-name
* To start swap ```swapon hdd-name```
* To stop swap ```swapoff hdd-name```
* make it permanent using UUID
```
UUID swap swap defaults 0 0
```
* ```swapon -a``` to mount fstab entry
* To create data lots of data (kachra)
1. of = output file
2. bs = blocksize
3. count = no of blocks
```
dd if=/dev/urandom of=file-name bs=10M count=100
```
* to extend lvm size with format extension as well
```
lvextend --size +1G /dev/vggroup-name/lv-name -r
```
* to increase the format size of lvm , if partition is already formatted with xfs
```
xfs_growfs # only for xfs type
```
* to increase the format size of any format
```
resize2f lvm-name
```
- For tunning purpose of machine
- Create a repo
[a] baseurl=ftp://192.168.10.254/pub/rhel8/AppStream gpgcheck=0 [b] baseurl=ftp://192.168.10.254/pub/rhel8/BaseOS gpgcheck=0
2. yum install tuned
* to check current administrator
tuned-adm active
* start the tuned services ``` systemctl start tuned```
* to get best adm ```tuned-adm recommended```
* to change adm ```tuned-adm profile name-of-list```
---
# Nice & Renice
1. nice is for giving Performance options to some task
2. if a new process starts it can be started with nice to provide with efficient performance resources ```nice -n -value process-name```
3. if process is already i action then renice command can be used ```renice -n -value process-id```
4. -20 stands for highest performance and +19 for lowest
5. ```ps -xl``` shows process list where NI is for Nice
6. To change nice value
7. Usage with respect to CPU can be checked
ps -aux --sort=pcpu
----
## In exam , two virual machines will be provided , so perform tasks as specified
* 122 is ip given by virtual machine when its connected with Base OS and its not accessible to all world
* World cannot directly access virtual machine , the network is accessed through Base OS
* always create password through ```passwd``` command only -- no reason
* crontab doesn't show actions or output of some command on terminal so it can be checked using I/O redirection
* ```watch date``` is command to start clock
* always restart service after changing config file of any services
* to install new kernel
rpm -ivh ftp-address-of-kernel-location i - > install , u - > update
* kernel installation process takes time so when this command is run ... wait until hostname is available to you by default ```ctrl C``` is prohibited in this action
* to check kernel when reboot is done .... more then 2 lines will be seen for kernel
* selinux is always updated only after reboot
* after reboot selinux relabels all files and gets persistent
----
## Enable IP Forwarding
* It is a feature of router with help of which ip of different series are able to communicate with each other
* two lan cards can communicate with each other when its ON
* run command
sysctl -a | grep -i ip_fo
* set net.ipv4.ip_forward = 1
* to make ip forwarding permanent,open
vim /etc/sysctl.conf
* write at end of sysctl.conf file
net.ipv4.ip_forward = 1
* to load new settings - > reads the sysctl.conf file and updates
sysctl -p
* 0 - > Disable 1 - > Enable
* to set it temporarily
sysctl net.ipv4.ip_forward = 1
----
## Archive
* for gzip --z --gz
tar -cvzf file.tar.gz file-to-make-tar
* for bzip2
tar -cjvf file.tar.bz2 folder-name
* for xz
tar -cJvf file.tar.xz folder-name
* to decompress files elsewhere, copy the tar in that directory and decompress it by
tar -xvf tar-name
* to decompress at certain path
tar -xvf tar-name -C path-name
----
## VDO -> Virtual Data Optimizer
* Minimum space requires = 15 to 20 GB
* maintins the copy of two or more copies
* the virtual size remains same and not increases even if same file is copied in the same folder again and again
* it is a optimizer and maintains if data is not duplicated
* for repo requires
baseurl=AppStream and BaseOS
* repo link will be provided by the examiner
* for installation
yum install vdo kmod-kvdo
* it is not a service
* to create a vdo
vdo create --name=vdo1 --device=/dev/vda --vdoLogicalSize=50G
* logical size can be greater then actual block device
* it is an dev mapper technology device <b>DM</b>
* to get information about vdo device
vdo status --name=particular-vdo-name
* to get all vdo devices list
vdo status
* to get list of vdo devices, uses 4GB for meta-data
vdostats --human-readable
* saving % denotes the amount of duplicated data
* to format
mkfs.xfs /dev/mapper/vdo1
* for mounting
mount /dev/mapper/vdo-name path-to-mount
* for fstab entry ,
/dev/mapper/vdo1 path-to-mount xfs defaults,x-systemd.requires=vdo.service 0 0
---
## AutoFs
* NFS -> Network File System is a object storage over the internet or intranet
* AutoFs is used to remove the mounting problem of Fstab raised for 1000 of users working in same community/organization
* to install Autofs
yum install autofs
* to start service
service autofs restart
* to view mount points
service autofs status
* after installing Autofs, we are provided with 2 files named
1. /etc/auto.master
2. /etc/auto.misc
* If you modify the /etc/auto.master configuration file while autofs is running, you must tell the automount daemon(s) to reload by
service autofs reload
* Work of autofs is done over a user server where N users can connect (using something like ssh) and access the NFS shared by main server
* You can also examine the ```/etc/rmtab``` file on the server to see how frequently its clients are mounting and unmounting automounted filesystems. When a filesystem is mounted, an entry is added to the ```/etc/rmtab file```
## Server Side
* create a nfs directory , add path is exports and make it shareable by ```exportfs -r```
* ```showmount -e ip-address``` will show the shareable directory path
## Client-Server Side
* Entry in auto.misc is something like
```
subdirectory-to-create-when-user-logs-in -fstype=nfs,rw,vers=3 server-ip/nameserver:path-of-nfs-to-mount
mynfs-directory -fstype=nfs,rw,vers=3 adhoc.example.com:/mnt/share
```
* This subdirectory is created dynamically by automount. It should not actually exist on the client machine.
* Entry in auto.master is something like
```
directory-to-mount-on /etc/auto.misc --timeout 60
```
----
# RHEL 8 exam tips ( NOTHING IS RIGID ... SAMEY KE SAATH PARIVARTAN NISHCHIT HAI )
1.
* Base OS = 7.5
* make sure to use base OS properly
* two OS will be provided one for partition problems, one for other
* names of virtual machines - > station1,station2 or node1,node2 or machine1,machine2 or system2,system4
2. <b> IP ADDRESS </b>
* series 172.23.10.3 netmask 255.255.255.0
* partition setup to be done ---- IP not to be set
* Non partition ---- IP set
* just reverse for password break
3.
* ifconfig not working , its replacement is ```ip a```
* there will be no ifcfg-eno1 file ---check the same file in your base OS
* SET IP Address graphically
1. in terminal if we run ```startx``` command GUI will be opened
2. open wired setting
3. click on + in wired
4. check on manual
5. Move top IPv4 and set all details
6. reboot