https://linuxize.com/post/vim-delete-line/
Esc key to go to normal mode.5dd and hit Enter to delete the next five lines.The basic steps to perform a search in Vim are as follows:
/.Enter to perform the search.n to find the next occurrence or N to find the previous occurrence.tecmint.com/tmux-to-access-multiple-linux-terminals-inside-a-single-console/
https://askubuntu.com/questions/850055/ctrl-b-c-n-w-etc-not-working-in-tmux-console
https://ostechnix.com/tmux-command-examples-to-manage-multiple-terminal-sessions
tmux
ctrl+b and Shift+% ::: Split Vertically
ctrl+b and Shift+" ::: Split Horizontally
Type "exit" from a particular window To kill that window/screen
ctrl+b and d ::: End Session
for example, to create a new terminal hold ctrl+b and release it then press shift+5 (%)
https://computingforgeeks.com/ext4-vs-xfs-complete-comparison/
https://www.tecmint.com/create-new-ext4-file-system-partition-in-linux/
mkfs.xfs /dev/device
mkfs.ext4 /dev/device
:::::: vi /etc/fstab ::::::
/dev/sdb /data xfs defaults,nofail 0 1
lsblk -f
lsblk -a
lsblk -i
df -h
getent is a Linux command that helps the user to get the entries in a number of important text files called databases
https://www.geeksforgeeks.org/getent-command-in-linux-with-examples/
stat - -format="%a" /path1/subdir
https://www.cyberciti.biz/faq/get-octal-file-permissions-from-command-line-on-linuxunix/
https://unix.stackexchange.com/questions/188674/how-to-get-file-permission-in-octal
To just see octal file permissions on a GNU/Linux:$ stat -c '%a' /etc/passwd
https://stackoverflow.com/questions/50904342/etc-passwd-vs-usr-bin-passwd
The two files are different, and serve different purpose.
/etc/passwd is user database (fun fact: contrary to its name, it doesn't store passwords - those are stored (possibly in hashed form) in /etc/shadow) - see man 5 passwd (i.e. passwd(5)), man 5 shadow (i.e. shadow(5)).
/usr/bin/passwd is utility that is supposed to modify user records stored in /etc/passwd and /etc/shadow. See man 1 passwd (i.e. passwd(1))
sudo pam_tally2 -u 703247699 --reset
https://stackoverflow.com/questions/5163144/what-are-the-special-dollar-sign-shell-variables
$1, $2, $3, ... are the positional parameters."$@" is an array-like construct of all positional parameters, {$1, $2, $3 ...}."$*" is the IFS expansion of all positional parameters, $1 $2 $3 ....$# is the number of positional parameters.$- current options set for the shell.$$ pid of the current shell (not subshell).$_ most recent parameter (or the abs path of the command to start the current shell immediately after startup).$IFS is the (input) field separator.$? is the most recent foreground pipeline exit status.$! is the PID of the most recent background command.$0 is the name of the shell or shell script.Most of the above can be found under Special Parameters in the Bash Reference Manual. There are all the environment variables set by the shell.
For a comprehensive index, please see the Reference Manual Variable Index.
sudo su interactive non-login shell.
sudo su - It is a login shell
To explain this you need to know what the programs do:
su - The command su is used to switch to another user (s witch u ser), but you can also switch to the root user by invoking the command with no parameter. su asks you for the password of the user to switch, after typing the password you switched to the user's environment.sudo - sudo is meant to run a single command with root privileges. But unlike su it prompts you for the password of the current user. This user must be in the sudoers file (or a group that is in the sudoers file). By default, Ubuntu "remembers" your password for 15 minutes, so that you don't have to type your password every time.bash - A text-interface to interact with the computer. It's important to understand the difference between login, non-login, interactive and non-interactive shells:Types of shells:
So the cases are:
sudo su Calls sudo with the command su. Bash is called as interactive non-login shell. So bash only executes .bashrc. You can see that after switching to root you are still in the same directory:
user@host:~$ sudo su
root@host:/home/user#
sudo su - This time it is a login shell, so /etc/profile, .profile and .bashrc are executed and you will find yourself in root's home directory with root's environment.
sudo -i It is nearly the same as sudo su - The -i (simulate initial login) option runs the shell specified by the password database entry of the target user as a login shell. This means that login-specific resource files such as .profile, .bashrc or .login will be read and executed by the shell.
sudo /bin/bash This means that you call sudo with the command /bin/bash. /bin/bash is started as non-login shell so all the dot-files are not executed, but bash itself reads .bashrc of the calling user. Your environment stays the same. Your home will not be root's home. So you are root, but in the environment of the calling user.
sudo -s reads the $SHELL variable and executes the content. If $SHELL contains /bin/bash it invokes sudo /bin/bash (see above).
scp -i mykey.pem somefile.txt root@my.ec2.id.amazonaws.com:/
https://stackoverflow.com/questions/6558080/scp-secure-copy-to-ec2-instance-without-password
setgid Creates a file using owner rather than user creating it
setuid sets the permission of execution
sticky bits - Accidental Delete Protection Bit
https://geek-university.com/linux/uid-user-identifier-gid-group-identifier/
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | processManagement:
fork: true
net:
bindIp: localhost
port: 27017
storage:
dbPath: /var/lib/mongo
systemLog:
destination: file
path: "/var/log/mongodb/mongod.log"
logAppend: true
storage:
journal:
enabled: true
|
https://www.tutorialspoint.com/unix/unix-using-variables.htm
https://www.serverlab.ca/tutorials/linux/administration-linux/how-to-set-environment-variables-in-linux/
export NAME=VALUE
export JAVA_HOME=/opt/openjdk11
unset VARIABLE_NAME
unset JAVA_HOME
::Listing All Set Environment Variables::
set
variable_name=variable_value
NAME="John Doe"
echo $NAME
readonly NAME
export NAME
Linux Variable Types
When a shell is running, three main types of variables are present −
Local Variables
Environment Variables
Shell Variables
https://www.2daygeek.com/lock-unlock-disable-enable-user-account-linux/
id <username>
passwd --status <username>
passwd -u <username>
usermod --unlock <username>