Linux Basic Command and Map

Process

all process ps -auxf

see all zombie process ps -aux | grep 'Z'

see systemd ps -p 1

SIGKILL –9 SIGKILL –15

kill -9 PID

Symlink & Hardlink

Symlink example:

ln original_file symlink1

for Read: readlink symlink1

for search find . -type l

for see inode stat original_file

Hardlink example:

ln original_file hardlink1

see number of inode ‘stat original_file’

see how many hardlinks find . -inum 672135

inode - inode is a data structure that stores information about a file or directory in a file system.

Hardlink its like original file

Hardlink -> inode <- file <- Symlink

Password

etc/password and etc/shadow

change password

passwd username

Group

were can find group etc/groupand password of groups etc/gshadow

sudo groupadd devops

sudo usermod -a -G devops username

delete group delgroup

name

Add users

useradd username -b /home/username -c "Username Usernamov" -g usergroup -p password

new command

adduser username

change home directory to user:

sudo usermod -d /home/evil -m username

delete userdel username

find someting..

whereis passwd

`ls -la /usr/bin/passwd

SUID GSID Sticky

USER + S(pecial)

Commonly noted as SUID, the special permission for the user access level has a single function: A file with SUID always executes as the user who owns the file, regardless of the user passing the command. If the file owner doesn’t have execute permissions, then use an uppercase S here.

Now, to see this in a practical light, let’s look at the /usr/bin/passwd command. This command, by default, has the SUID permission set:

[tcarrigan@server ~]$ ls -l /usr/bin/passwd 
-rwsr-xr-x. 1 root root 33544 Dec 13  2019 /usr/bin/passwd

Note: the s where x would usually indicate execute permissions for the user.\

command chmod u+s file

Group + S(pecial)

Commonly noted as SGID, this special permission has a couple of functions:

If set on a file, it allows the file to be executed as the group that owns the file (similar to SUID)
If set on a directory, any files created in the directory will have their group ownership set to that of the directory owner

[tcarrigan@server article_submissions]$ ls -l 
total 0
drwxrws---. 2 tcarrigan tcarrigan  69 Apr  7 11:31 my_articles

This permission set is noted by a lowercase s where the x would normally indicate execute privileges for the group. It is also especially useful for directories that are often used in collaborative efforts between members of a group. Any member of the group can access any new file. This applies to the execution of files, as well. SGID is very powerful when utilized properly.

As noted previously for SUID, if the owning group does not have execute permissions, then an uppercase S is used. command: chmod g+s directory

Other + t (sticky) The last special permission has been dubbed the “sticky bit.” This permission does not affect individual files. However, at the directory level, it restricts file deletion. Only the owner (and root) of a file can remove the file within that directory. A common example of this is the /tmp directory:

[tcarrigan@server article_submissions]$ ls -ld /tmp/
drwxrwxrwt. 15 root root 4096 Sep 22 15:28 /tmp/

The permission set is noted by the lowercase t, where the x would normally indicate the execute privilege.

command ‘chmod +t directory’

Programs for working with packages

internal:

see all packages in system

dpkg -l

search packages in system

dpkg -s firefox-dbg

know what files

dpkg -s

what files belong to the package

dpkg -L openssh-client

for install dpkg -i program.deb for remove dpkg -r program.deb

search package

apt-cache search telegram

for search version of package

apt-cache policy openssh-client

and install version 1.8 apt-get install openssh-client=1.8

link from where download files

cat etc/sources.list

Systemd

where usr/lib/systemd/system

all units systemctl list-units for service systemctl list-units type=service

reload after change systemctl daemon-reload

for see logs systemctl -u unitname

Create unit in systemd

nano etc/systemd/system/apt.updater.service

[Unit]
Description=Example of Systemd Unit

[Service]
Type=oneshot
ExecStart=apt-get update

[Install]
WantedBy=multi.user.target

Create unit in systemd timer

nano etc/systemd/system/apt.updater.timer

[Unit]
Description=Runs apt-get update every hour

[Timer]
onUnitActiveSec=1h
Unit=apt-updater.service

[Install]
WantedBy=multi.user.target

Mount disk iso

sudo mkdir /media/ubuntu_iso 

sudo mount /home/victor/Downloads/ubuntu-20.04.2-live-server.amd64.iso /media/ubuntu_iso/ -o loop

see mount disk df -h advanced mount | grep ubuntu_iso

echo "123456" > file 

dd if=file

img from disk

dd if=/dev/sda1 of=sda1.img bs=4096

bs - block of file = 4096 kb

delete all files with zero 0000000000000

dd if=/dev/zero of=/dev/sdx bs=4096

Mount hardisk

see all partition fdisk -l

sudo fdisk /dev/sdb

m - see all command
g - create new GPT partition table
w - write

to create ext4

sudo mkfs.ext4 -F /dev/sdb1

mount manual but after restart will disappear

sudo mkdir /media/data/

sudo mount /dev/sdb1/ /media/data/

to auto mount after restart, to know UUID sudo blkid

sudo  nana /etc/fstab/

.deb

see in deb package

ar t package.deb

tar.xz - its zip arhive

see in archive files

ar p package.deb debian-binary

for see tar.zx files

ar p package.deb debian.tar.xz | tar -tv -J

unzip arhive

ar x package.deb

unzip archive tar.xz

tar xfv control.tar.xz

Create .deb

fist

sudo apt install dh-make devscripts

create need folder

mkdir mvdir-0.1

need in directory

cd mvdir

copy file mvdir.sh to folder mvdir-01

cp ../../mvdir.sh .

edit bashrc

nano /home/dan/.bashrc

add it and save

export CITY=Jerusalem
export DEBMAIL="dan@local"
export DEBFULLNAME="Dan"

run command source and for test echo $DEBMAIL

source /home/dan/.bashrc

for make sample deb need run in your folder mvdir-01

dh_make --indep --createorig

indep - its be run for all system linux where have bash
createorig - the file specified with -f is copied in place. If no -f is supplied either but --createorig is, the current directory is created into a new archive

you can see new file in folder and remove all .ex files rm *.ex and rm README

now need create new file nano install and write:

mvdir.sh usr/bin/

if we have many bash scripts use *.sh usr/bin

for change file changelog use command dch

for build .deb

debuild -us -uc

-us - unsigned source it instructs no to sign the source files of the package with gpg key before create the package
-uc - unsigned changes it instructs no to sign changelog files before creating the package

to install deb package to remove -r

sudo dpkg -i  package.deb

Sign package deb

to create keys

gpg --gen-key

to change and update version of changelog file.(achtung! email and name must be the same gpg-keys)

dch -i

-i - increment update change version of changelog

see gpg keys

gpg --list-keys

now sign build package

debuild -b

to export gpg key

gpg --export -a "dan@local" > public.key

Monitoring and Proc

see version linux or uname -a uname take information from:

cat /proc/version

see cpu info

cat /proc/cpuinfo

see time online

cat /proc/uptime

see devices

cat /proc/devices

see what filesystems support

cat /proc/filesystems

see all mounts

cat /proc/mounts

see mem and swap ram

free -h

oom killer score s

cat /proc/13/oom_score_adj

iftop to see internet traffic

iftop

Ports

see if port 8080 open

netstat -lptun | grep 8080

Firewall

Iptables

see all rules :

sudo iptables -L

for all rules and numbers and tables

sudo iptables --line-numbers -L -v -n

see rules only input :

sudo iptables -L INPUT

all packet drop from 10.10.10.10

sudo iptables INPUT -s 10.10.10.10 -j DROP

all packet go to 10.10.10.10 drop

sudo iptables OUTPUT -s 10.10.10.10 -j DROP

all packege drop to 10.10.10.0/24

sudo iptables OUTPUT -s 10.10.10.0/24 -j DROP

all packet from 10.10.10.10 be drop to port 22

sudo iptables -A INPUT -p tcp --dport 22 -s 10.10.10.10 -j DROP

to accept all

sudo iptables -P INPUT ACCEPT

disable ICMP answer

sudo iptables -A INPUT -p icmp --icmp-type 8 -j DROP

for delete rules:

sudo iptables -D s 10.10.10.0 =j DROP

all clean rules:

iptables -F

Iptables persistent

we need iptables-persistent for be save after restart:

install

apt install iptables-persistent

run and save rules

sudo service netfilter-persistent save

to see changes netfilter file

cat /etc/iptables/rules.v4

to restore all rules in file

iptables-restore < /etc/iptables/rules.v4

sudo sh -c "iptables-restore < /etc/iptables/rules.v4"

NAT forward

linux2

to destination

iptables -t nat -A PREROUTING -p tcp -d 192.168.0.2 --dport 80 -j DNAT --to-destination 192.168.0.3:80

to source

iptables -t nat -A POSTROUTING -p tcp -d 192.168.0.3 --dport 80 -j SNAT --to-source 192.168.0.2:80

to source use masquerade

iptables -t nat -A POSTROUTING -p tcp -d 192.168.0.3 MASQUERADE

MAIL

Simple Command

Delete

delete files and folder

rm -rf <folder>

Program Dependencies

ldd /usr/bin/bash

Tree

tree folder/

all tree process

sudo pstree

dmidecode is a tool for dumping a computer’s DMI (all hardware about machine)

dmidecode

System_Commands

List the file/folder in the current directory.

ls

List files/folders in a current directory in detailed format.

ls -larth

Shows detailed information about the file or directory.

stat <fileName/dirName>

View calendar.

cal

Shows the name of the system host.

hostname

Shows the host id of the system assigned by the OS.

hostid

Show the current data and time in UTC format

date

Shows the currently logged-in username of the terminal.

whoami

Shows the elapsed time duration since the machine logged in.

uptime

Unix name.

uname

Clears the screen.

clear

Lists all the commands executed until now.

history

Super User Do

sudo -i

Shows the exit status of the last executed command (0 — success, 1–255 — error/failure).

echo $?

Restart the machine immediately (-r restart).

shutdown -r now

Displays all the environment variables of the Linux system.

printenv

Shows previous logins in the Linux system.

Last

Directory Commands

Shows the present working directory (abbr. Print Working Directory).

pwd

Change directory.

cd

Changes to its parent directory (i.e.) one level up.

cd ..

Change to the directory mentioned.

cd <dirName>

Changes to the currently logged-in user’s home directory.

cd ~ or cd

Changes the directory two levels up.

cd ../..

Changes to the last working directory.

cd

Creates the directory.

mkdir <dirName>

Creates a directory with its parent directories if it does not exist (-p parent).

mkdir -p <pathOftheDir>

File Commands →

Creates an empty file or updates the timestamp of the existing file.

touch

Creates a single empty file.

touch <fileName>

Creates file1, file2 empty files.

touch <file1> <file2>

Concatenates and displays the contents of files.

cat

Displays the contents of the file.

cat <fileName>

Creates a new file, allows to input content interactively and redirects inputted content to the created file (> redirection operator).

cat > <fileName>

Displays first 10 lines of the file by default.

head <fileName>

Displays first 5 lines of the file (-n number)

head -n 5 <fileName>

Displays the last 10 lines of the file by default.

tail <fileName>

Displays last 5 lines of the file (-n number).

tail -n 5 <fileName>

Displays contents of the file in real-time even when the file is rotated or replaced (used for log file monitoring).

tail -F <fileName>

Used to view large files (log files) in a paginated manner.

less <fileName>

rm — remove commands

Removes the file.

rm <fileName>

Removes files & folders of directory recursively (-r recursive).

rm -r <dirName>

Force remove the files & folders of directory recursively (-f force).

rm -rf <dirName>

cp — copy commands

Copy the files and folders from source to destination.

cp <source> <destination>

Copy dir1 directory to dir2 directory recursively (-r recursive).

cp -r <dir1> <dir2>

Move or rename commands

mv

mv <fileName> <newFileName> — renames the file to a new name.

Moves the file to new path.

mv <oldFilePath> <newFilePath>

File Permission Commands

Changes mode/permissions of the file.

chmod <octalNumber> <fileName>

Changes mode/permissions of the directory recursively.

chmod <octalNumber> -R <dirName>

Changes the user ownership of a file.

chown <newUser> <fileName>

Changes the user & group ownerships of a file.

chown <newUser>:<newGroup> <fileName>

Updates the group name for file/directory.

chgrp <groupName> <fileName/dirName>

Shows the file/directory access control list.

getfacl <fileName/dirName>

Modifies the current acl of the file/directory.

setfacl -m u:<userName>:rwx <fileName/dirName>

Removes the acl permissions for the file/directory.

setfacl -x u:<userName>: <fileName/dirName>

Modifies the group acls for the file/directory.

setfacl -m g:<groupName>:rwx <fileName/dirName>

Removes the group acl permissions for the file/directory.

setfacl -x g:<groupName>: <fileName/dirName>

File Permission Octal Numbers read (r) — 4, write (w)- 2, execute (x) — 1 => chmod 777 < file /folder_name >

User Management Commands →

Creates a user account.

useradd

Creates user account without home & mail spool directories.

useradd <userName>

Creates user account with home & mail spool directories.

useradd -m <userName>

Creates a password for the user and stores it in /etc/shadow file.

passwd <userName>

User delete.

userdel

Deletes the user from the system.

userdel <userName>

Deletes the user from the system along with home and mail spool directories (-r remove).

userdel -r <userName>

Stores information about user accounts.

/etc/passwd

Displays the complete list of users on that machine.

cat /etc/passwd

Stores the password for users in an encrypted format.

/etc/shadow

Displays the complete list of user passwords on that machine.

cat /etc/shadow

Substitute user.

su

Switches to the user mentioned.

su <userName>

To log out from that user.

exit

Modify user.

usermod

Adds the user to another group (-aG append the user to the group without removing from other groups).

usermod -aG <groupName> <userName>

Change shell.

chsh

Changes the shell to bash for the user.

chsh -s /bin/bash <user>

Changes the shell to sh for the user.

chsh -s /bin/sh <user>

Group Management Commands →

Creates the group.

groupadd <groupName>

Delete the group.

groupdel <groupName>

Stores the information of the groups.

/etc/group

Displays the complete list of groups on that machine.

cat /etc/group

Creates a password for the group.

gpasswd <groupName>

Adds the user to the group.

gpasswd -a <userName> <groupName>

Removes the user from the group.

gpasswd -d <userName> <groupName>

Adds multiple users to the group and removes the existing ones of the group.

gpasswd -M <userName1>,<userName2>,<userName3> <groupName>

Searching Commands →

Used to search for files/directories based on names.

locate

Updates the database so the results are up-to-date.

sudo updatedb

Locates the file/directory and displays the path.

locate <fileName/dirName>

GREP Command s— Global Regular Expression Print →

Used to find text patterns within files.

grep <textToSearch> <fileName>

Used to find text patterns within the file ignoring the case (-i ignore case).

grep -i <textToSearch> <fileName>

Used to find non matching lines of text patterns (-v invert-match).

grep -v <textToSearch> <fileName>

Used to display the matching string file names.

grep -l <textToSearch> <fileNames>

Find Commands →

Finds the mentioned file if available in the current directory (.(period) represents current directory).

find. -name <fileName>

Finds the mentioned file in the directory.

find <dirName> -name <fileName>

Finds the files in the directory having 754 permission.

find <dirName> -perm 754

Hardware Commands →

Shows systems memory information ( -h human-readable format).

free -h

Shows the disk space usage of mounted file systems.

df -h

Disk usage.

du

Displays disk usage information (-h human-readable format).

du -h

Displays the total size of the directory instead of individual files in human-readable format (-s summarize).

du -sh

Displays the total size of the file/directory.

du -sh <fileName/dirName>

Network Commands →

Tests the reachability & responsiveness of the remote host.

ping <hostName>

Shows DNS information of the domain.

dig <domainName>

Used to retrieve/download files from the internet.

wget <url>

Used to retrieve/download files from the internet.

curl <url>

Display available network interfaces.

ifconfig

Display and manipulate network interface info.

ip addr

Shows the public IP address of the machine.

curl ifconfig.me

Shows all TCP open ports (-a all, t-tcp, n-active, p protocol).

netstat -antp

Traces the route using packets from source to destination host.

traceroute <url>

Process Info Commands →

ps — process status.

Shows the currently running process.

ps

Shows the process of the username

ps -u <userName>

Shows all the processes of the system.

ps -ef

Shows the real-time, dynamic view of the running processes of a system.

top

Gracefully terminates the process pid.

kill <pid>

Shows process ID of processes based on name/other criteria.

pgrep <processName>

Background, sends the process to the background & continues execution without interruption.

bg

foreground, brings the process to the foreground and makes it an active process.

fg

No hangup, runs command/script in the background even after the terminal is closed or the user logs out.

# nohup

Archiving File Commands →

Tape archive.

tar

Creates the tar file with the fileName for the directory mentioned (-c create, -v verbose, -f output file name).

tar -cvf <fileName> <directory>

tar -xvf <sourceTarFileName> -C <destinationDir>

Package Manager — LINUX DISTROS

apt — Package Manager for Debian-based Linux distributions Eg: Ubuntu.
yum — Package Manager for Redhat-based Linux distributions Eg: Amazon_Linux.

Repository

Disable

sudo apt-get update --allow-unauthenticated

sudo apt-get update --allow-insecure-repositories

Crontab

0 12 1 * * /opt/wordpress/tls_renew.sh >> /var/log/cron.log 2>&1
# *  *  *  *  *
# |  |  |  |  |
# |  |  |  |  |
# |  |  |  |  +-------------------- day of week [0 - 6] [Sunday=0]
# |  |  |  +-------------------- month [1-12]
# |  |  +--------------------- day of month [1-31]
# |  +---------------------- hour [0-23]
# +----------------------- min [0-59]

edit

crontab -e

list

crontab -l

edit other user root

crontab -eu root

Systemd Timer

Option

OnActiveSec= Defines a timer relative to the moment the timer unit itself is activated. OnBootSec= Defines a timer relative to when the machine was booted up. In containers, for the system manager instance, this is mapped to OnStartupSec=, making both equivalent. OnStartupSec= Defines a timer relative to when the service manager was first started. For system timer units this is very similar to OnBootSec= as the system service manager is generally started very early at boot. It’s primarily useful when configured in units running in the per-user service manager, as the user service manager is generally started on first login only, not already during boot. OnUnitActiveSec= Defines a timer relative to when the unit the timer unit is activating was last activated. OnUnitInactiveSec= Defines a timer relative to when the unit the timer unit is activating was last deactivated.

1.Create the file /etc/systemd/system/helloworld.service with the following content:

[Unit]
Description="Hello World script"

[Service]
ExecStart=/usr/local/bin/helloworld.sh

[Install]
WantedBy=multi-user.target

2.Create the file /etc/systemd/system/helloworld.timer with the following content:

[Unit]
Description="Run helloworld.service 5min after boot and every 24 hours relative to activation time"

[Timer]
OnBootSec=5min
OnUnitActiveSec=24h
OnCalendar=Mon..Fri *-*-* 10:00:*
Unit=helloworld.service

[Install]
WantedBy=multi-user.target

This is the timer file that controls the activation of the respective service file.

3.Verify that the files you created above contain no errors:

systemd-analyze verify /etc/systemd/system/helloworld.*

4.Start the timer:

sudo systemctl start helloworld.timer

5.Enable the timer to make sure that it is activated on boot

sudo systemctl start helloworld.timer

from cron to systemd

Cron     : systemd timer
-------- : ----------------------------
@reboot  : OnBootSec=1s
@yearly  : OnCalendar=*-01-01 00:00:00
@annually: OnCalendar=*-01-01 00:00:00
@monthly : OnCalendar=*-*-01 00:00:00
@weekly  : OnCalendar=Sun *-*-* 00:00:00
@daily   : OnCalendar=*-*-* 00:00:00
@hourly  : OnCalendar=*-*-* *:00:00

Getting e-mail notifications when a timer fails

In the following example, we are using the mailx command from package mailx. It requires the Postfix e-mail server to be installed and correctly configured.

Create the script /usr/local/bin/send_systemd_email.

The script requires two parameters: $1, the e-mail address, and $2, the name of the service file for which the failure notification is received. Both parameters are supplied by the unit file running the mail script.

#!/bin/sh
systemctl status --full "$2" | mailx -S sendwait\
 -s "Service failure for $2" -r root@$HOSTNAME $1

Make sure the script is executable:

sudo chmod 755 /usr/local/bin/send_systemd_email

Create the file /etc/systemd/system/[email protected].

[Unit]
Description=Send systemd status information by email for %i to USER

[Service]
Type=oneshot
ExecStart=/usr/local/bin/send_systemd_email EMAIL_ADDRESS %i
User=root
Group=systemd-journal

Replace USER and EMAIL_ADDRESS in the file with the login and e-mail address of the user that should receive the e-mail. %i is the name of the service that has failed (it is passed on to the e-mail service by the %n parameter).

Verify the service file and fix the reported issues: systemd-analyze verify /etc/systemd/system/[email protected]


Verify the service file and fix the reported issues:
```bash
sudo systemctl start [email protected]

If the command returns no output, the file has passed the verification successfully.

To verify the complete procedure, start the service using the dbus instance for testing. (You can use any other service that is currently running. dbus is used in this example because the service is guaranteed to run on any installation.)

sudo systemctl start [email protected]

If successful, EMAIL_ADDRESS receives an e-mail with the subject Service failure for dbus containing dbus status messages in the body. (This is just a test, there is no problem with the dbus service. You can safely delete the e-mail, no action is required).

If the test e-mail has been successfully sent, proceed by integrating it into your service file.

To add an e-mail notification to the service, add an OnFailure option to the Unit section of the service file for which you would like to get notified in the event of failure:

[Unit]
Description="Hello World script"
OnFailure=send_email_to_USER@%n.service

[Service]
ExecStart=/usr/local/bin/helloworld.sh

The e-mail service file has the recipient’s e-mail address hard-coded. To send notification e-mails to a different user, copy the e-mail service file, and replace the user login in the file name and the e-mail address within the copy.

To send a failure notification to several recipients simultaneously, add the respective service files to the service file (use spaces as a separator):

OnFailure=send_email_to_tux@%n.service send_email_to_wilber@%n.service