Usefull commands
Version 2025.7.9.

man command - display documentation about command.
Find string in documentation: man -K string
info - read info documents.

whatis - show one line command description.
Find commands by pattern: whatis -w 'pattern'
List all basic commands: whatis -s 1 -w '*'
List all commands: whatis -s 1,8 -w '*'
1 is section for basic commads. 8 is section for administrative commads.

cat - concatenate files and print on the standard output.
cd - change the working directory.
ls - list directory contents.
pwd - print name of current directory.
cp - copy files.
mv - move files.
mkdir - make directories.

bc - calculator.
date - display the date and time.
date -I - displays date that is useful when create file with name as current date.
runlevel - output previous and current runlevel.
fdisk - manipulate disk partition table.
free - display amount of free and used memory in the system.
gcc - C compiler.
g++ - C++ compiler.
grep - search a file or stdin for a pattern.
look - display lines beginning with a given string.
head - output the first part of files or stdin.
tail - output the last part of files or stdin.
seq - print a sequence of numbers.
iconv - convert text from one character encoding to another.
Convert file from cp1251 to utf8: iconv -f cp1251 -t utf8 file_name -o file_name
md5sum - print or check MD5 checksums.
umount - від’єднати файлову систему.
env - show environment variables.
pgrep, pkill - look up or signal processes based on name and other attributes.
read - read a line from stdin.
sleep - suspend execution for an interval.
sort - sort lines of text files (or stdin).
tee - read from stdin and write to stdout and files.
top - display Linux tasks.
xset - user preference utility for X.
nsloookup - запитати IP-адресу в DNS, вивести адресу DNS.
file - determine file type.
ldd - print shared library dependencies.
Get string md5sum: md5sum <<< 'string'
Get file md5sum: md5sum file_name
Generate initramfs image for current kernel: dracut --force
Switch monitor to standby mode: xset dpms force standby
Show command execution time: time command
Compare files: cmp file1_name file2_name
Compare files: diff file1_name file2_name
cmp and diff can also compare binary files.
Compare directories: diff -r directory1_path directory2_path
Find wifi access points: iwlist scan
Check mail sending: echo 'Check.' | mail -s Check sergiyvovk69@gmail.com
Connect to FTP or SFTP server: lftp -u user_name server_address
Connect to FTP server: ftp server_address
Show devices space usage and mount points: df -h
Show specified device space usage: df -h device_or_mount_point
Show current directory size: du -hs
Show directory size: du -hs directory
Show total size of files or directories: du -ch file1/directory1 file2/directory2 ...
Show messages from kernel: dmesg
Print uptime and load: uptime

Make symlink: ln -sv target link_name
Make symlink in current directory: ln -sv target
Make symlinks in directory: ln -sv targets_list directory

Show current locale: locale
List locales: locale -a
Run application with specified locale: LANG="locale_name" application
The locale for user may be set in ~/.bashrc file. Example: export LANG="uk_UA.utf8"

fsck - check and repair a Linux file system.
Check ext2/3/4 file system: sudo e2fsck -v device
Force check ext2/3/4 file system: sudo e2fsck -v -f device
Check blocks on ext2/3/4 file system: sudo e2fsck -v -f -c device
Check fat32 file system: sudo fsck.vfat device
Check ntfs file system: sudo ntfsck device
Check xfs file system: sudo xfs_repair -v device
Check exfat file system: sudo exfatfsck device

Reboot computer: shutdown -r now
Power off computer: shutdown now

Encode string to base64: <<< 'string' base64
Decode string from base64: <<< 'base64_string' base64 -d

Encrypt string by password: <<< 'string' openssl enc -e -a -aes-128-ctr -nopad -nosalt -k password
Decrypt string: <<< 'crypted_string' openssl enc -d -a -aes-128-ctr -nopad -nosalt -k password
Опції -nopad, -nosalt не обовязкові але дозволяють отримати компактніший вивід.
Отримати список алгоритмів шифрування: openssl enc -ciphers
-aes-128-ctr це один з аглоритмів шифрування.
Завдяки -a вивід буде стрічкою а не двійковий.
Якщо -k password не задати, пароль запитається в терміналі.

Encrypt file: openssl enc -e -aes-128-ctr -k password -in input_file -out output_file
Decrypt file: openssl enc -d -aes-128-ctr -in input_file -out output_file

Some openssl enc command options:
-help          Display options summary
-e             Encrypt
-d             Decrypt
-a             Base64 encode/decode
-base64        Same as -a
-in infile     Input file
-out outfile   Output file
-k value       Passphrase
-kfile infile  Read passphrase from file

Generate key: openssl rand -base64 length
Generate key to file: openssl rand -base64 -out file length
Generate hex key: openssl rand -hex length

Create disk image: dd if=device of=file.img
Create disk image, skip errors: dd if=device of=file.img conv=noerror
Write image file to disk: dd if=file.img of=device
Create 10 * 2 mb file with zero bytes: dd if=/dev/zero of=file_name bs=10M count=2
Create file with 512 zero bytes: dd if=/dev/zero of=file_name bs=512 count=1
Create file with 512 random bytes: dd if=/dev/urandom of=file_name bs=512 count=1
Mount image file: mount -o loop file.img /mnt/image

Write the iso image with linux to usb stick:
umount /dev/sdX*
sudo dd if=iso_image_file of=/dev/sdX bs=8M status=progress oflag=direct
X is the usb stick letter.

Get directory checksum:
rhash -r --md5 directory | sort | md5sum

Create 10 gb qcow2 disk image:
qemu-img create -f qcow2 file_name.qcow2 10G

Convert qcow2 disk image to raw:
qemu-img convert -f qcow2 -O raw input_file.qcow2 output_file.img

Convert raw disk image to qcow2:
qemu-img convert -f raw -O qcow2 input_file.img output_file.qcow2

Show firewall settings: sudo firewall-cmd --list-all

Enable port:
sudo firewall-cmd --permanent --add-port=port_number/tcp
sudo firewall-cmd --reload

List swaps: swapon --show
Activate swap: swapon device_or_file
Dectivate swap: swapoff device_or_file
Примітка. Live Fedora може підключити swap /dev/mapper/fedora-swap автоматично якщо він існує.

The example of creating swap file:
dd if=/dev/zero of=/swapfile bs=10M count=50
mkswap /swapfile
chmod -v 600 /swapfile

Show ext2/3/4 file system label: e2label device
Set ext2/3/4 file system label: e2label device label

Show lines that is in list1.txt but not in list2.txt:
diff list1.txt list2.txt | grep '^< ' | sed 's/^< //'

watch - repeat command and show output.

screen - screen manager with VT100/ANSI terminal emulation.
ctrl a ?: довідка про клавіши.
ctrl a c: запустити нову копію bash.
ctrl a d: відключитись від програми screen.
ctrl a ": показати список запущених програм через який можна перейти на іншу програму.
ctrl a 0-9: перейти на програму під введеним номером.
C-a k: destroy current window.
Запустити команду у програмі screen: screen команда
Запустити команду у програмі screen і відключитись від неї: screen -d -m команда
Показати список сеансів: screen -ls
Перейти до сеансу: screen -r імя_сеансу
Перейти до останього сеансу: screen -R
Виконати на сервері ssh команду у програмі screen:
ssh -t імя_користувача@адреса_серверу 'screen команда'
Після цього для відключення від серверу ssh можна натиснути ctrl a d.
Перейти до останього сеансу програми screen на сервері ssh:
ssh -t імя_користувача@адреса_серверу 'screen -R'

Job control:
Зупинити процес і поверутись в командний рядок можна клавішами ctrl + z.
Запустити команду в фоні: команда &
Продовжити процес в фоні; bg [ %номер ]
Продовжити процес в фоні; %номер &
Повернутися до процесу: fg %номер
Повернутися до процесу: %номер
Повернутися до останього процесу: fg
Отримати список запущених задач: jobs

nohup - run a command immune to hangups, with output to a non-tty.
Запустити команду в фоновому режимі так щоб вона не завершилась після закритя терміналу або завершення скрипту можна таким чином:
nohup команда > /dev/null &

Run program and return to terminal:
(program &> /dev/null &)
The program will not be closed if user will close the terminal.
The same effect may be achieved by nohup command.

Scan current directory for virus: clamscan -ir
Scan directory for virus: clamscan -ir directoty_path
Update clamav virus database: sudo freshclam

scp — remote file copy program.

Generate ssh key: ssh-keygen -t rsa
Generate private ssh key to file: ssh-keygen -t rsa -f file-name
The public key will be saved to file-name.pub.

Specify port for ssh: ssh -p port user@host
Specify private ssh key file for ssh: ssh -i key-file user@host

Add ssh key:
ssh-copy-id user@host
ssh-copy-id -p port user@host
ssh-copy-id -i key-file user@host
key-file це публічний ключ.
Якщо приватного ключа немає в одній папці з публічним ключем, можна використати команду:
ssh-copy-id -f -i key-file user@host

The public ssh key file can be added to the end of ~/.ssh/authorized_keys file.
Sample: cat key-file >> ~/.ssh/authorized_keys

Run graphic program by ssh: ssh -X user_name@server_address program_name

Sample of SSH tunel creating:
ssh -L 5432:localhost:5432 -N -f -l simple_user vps2.happyuser.info
ssh -L 5432:localhost:5432 -N simple_user@vps2.happyuser.info
ssh -L 5900:localhost:5900 -N -f -l lim -p 3645 178.95.250.72
-N : do not execute command on remote host.
-f : background mode.
-l : login.
-p : port.

Sample of reverse SSH tunel creating:
ssh -R 9080:localhost:9080 -N -l simple_user vps2.happyuser.info
ssh -R 9080:localhost:9080 -N simple_user@vps2.happyuser.info
An access to port 9080 on a server will be local.

Sample 2 of reverse SSH tunel creating:
ssh -R '*:3005:localhost:3000' -N -l gateway vps2.happyuser.info
ssh -R '*:3005:localhost:3000' -N gateway@vps2.happyuser.info
ssh -R vps2.happyuser.info:3005:localhost:3000 -N gateway@vps2.happyuser.info
ssh -R 95.85.37.18:3005:localhost:3000 -N gateway@95.85.37.18
This allows external access to a server on port 3005 which will be redirected to
a local port 3000 and requires
"GatewayPorts yes" or "GatewayPorts clientspecified" in /etc/ssh/sshd_config on a server.

Sample of how to measure the download speed of SSH channel:
ssh simple_user@vps2.happyuser.info cat /dev/urandom | dd of=/dev/null status=progress

Sample of how to measure the upload speed of SSH channel:
< /dev/urandom ssh simple_user@vps2.happyuser.info dd of=/dev/null status=progress

Split string sample: grep -Eo '[^,]+' <<< 'string1,string2,string3'
Each element will be get as separate line.

Get first element: grep -Eo '^[^,]+' <<< 'string1,string2,string3'
Get last element: grep -Eo '[^,]+$' <<< 'string1,string2,string3'
Get list element sample: cut -d, -f3 <<< 'string1,string2,string3,string4'
Replace spaces by \n: tr ' ' '\n' <<< '1 2 3 4 5'
Delete spaces in string: tr -d ' ' <<< '1 2 3 4 5'

Get subexpression sample: sed -r 's/^.*:(.*),.*$/\1/' <<< 'string1:string2,string3'
Enclose strings between quotes: echo -e "string 1\nstring 2\nstring 3" | sed "s/.*/'&'/"
The detailed samples about sed is in sed_sample.sh file.

Show hexadecimal values of string bytes: echo -n "string" | od -t x1
Redirect standard output and standard error to /dev/null: command &> /dev/null

Create iso image: genisoimage -R -o iso_file_name directory_path
Look for useable CD/DVD devices: wodim --devices dev='/dev/cdrom'
Print CD/DVD drive capabilities: wodim -prcap dev='/dev/cdrom'
Print CD/DVD drie inquiry information: wodim -inq dev='/dev/cdrom'
Blank the entire CD/DVD-RW disk: sudo wodim -v blank=all -eject dev='/dev/cdrom'
Minimally blank CD/DVD-RW disk: sudo wodim -v blank=fast -eject dev='/dev/cdrom'
Record CD/DVD from iso image: sudo wodim -v -eject dev='/dev/cdrom' iso_file_name
Record CD/DVD from directory: genisoimage -R directory_path | wodim -v fs=6m speed=2 dev='/dev/cdrom' -
Eject CD/DVD: eject /dev/cdrom

Example of connection to VNC server via SSH tunnel:
vncviewer -via taras@188.226.157.20 localhost::5901

Show information about video or audio: ffprobe input_file

Encode video or audio: ffmpeg -i input_file output_file
Имя вихідного файлу залежить від його розширення.

To specify the target bitrate for video and audio, use the -b:v and -b:a options, respectively. You can use abbreviations like K for kBit/s and M for MBit/s.
Example: ffmpeg -i input.mp4 -b:v 1M -b:a 192K output.avi

Install tesseract: sudo dnf install tesseract tesseract-langpack-ukr gimagereader-gtk
The gimagereader-gtk is frontend for tesseract.
Recognize english text on the picture: tesseract picture.png stdout
Recognize english text on the picture and output result to out.txt: tesseract picture.png out
Recognize ukrainian text on the picture: tesseract picture.png stdout -l ukr
Recognize english and ukrainian text on the picture: tesseract picture.png stdout -l eng+ukr

Set host name: hostnamectl set-hostname host_name

Get the file from internet and write to standart output: curl -s file_address
Download the file from internet: curl -o file_name file_address

Execute string as JavaScript: node -e "string"
Execute string as PHP: php -r "string"

Check ports: netstat -atnp|grep LISTEN

List estabilished and listened TCP sockets: ss -atn
List estabilished and listened TCP sockets with its processes: ss -atnp
List estabilished TCP sockets: ss -tn
List listened TCP sockets: ss -ltn
-a : estabilished and listened sockets.
-l : listened sockets.
-t : TCP sockets.
-p : show sockets processes.
-n : show ports numbers instead of services names.

nmap 192.168.1.2-254
Scan ports: nmap -p1-65535 localhost

Find files by name: locate pattern
Find files by name, ignore case: locate -i pattern

find - find files in current directory.
find directory - find files in directory.
find -iname '*.txt' - find files with txt extension in current directory.
find directory -iname '*.txt' - find files with txt extension in directory.
find sample by "or" operator: find -name '*.jpg' -o -name '*.png'
find -name pattern - case sensitive search by file name in current directory.

mkfs - build a Linux filesystem.

Format partiion to ext4 file system: sudo mkfs.ext4 -L label device

Format partiion to fat32 file system: sudo mkfs.vfat -n label device

Format partiion to ntfs file system: sudo mkfs.ntfs -L label device
-f : fast format.

Format partition to exfat file system: sudo mkfs.exfat -n label device

mount - приєднати файлову систему.
Показати список зионтованих файлових систем: mount без опцій.
Mount ext4 filesystem: mount -t ext4 device directory_path
Mount ext4 filesystem for read only: mount -r -t ext4 device directory_path

Mount ftp: curlftpfs ftp://user:password@host directory
Unmount ftp: fusermount -u directory

Sample:
mkdir /tmp/android-ftp
curlftpfs ftp://android:android@192.168.1.29:2221 /tmp/android-ftp
fusermount -u /tmp/android-ftp

Show EFI boot configuration: efibootmgr
Shedule next boot configuration: efibootmgr -n configuration_number

zenity - display GTK+ dialog.
Display file selection dialog: zenity --file-selection
Display notification: zenity --notification --text='Nnotification.'
Display info dialog: zenity --info --text='Message.'
Display error dialog: zenity --error --text='Message.'
Display warning dialog: zenity --warning --text='Message.'
Display question dialog: zenity --question --text='Question.'
Display password dialog: zenity --password
Display text entry dialog: zenity --entry --text='Message.'

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                                             Archivators

Create archive:
tar cvzf ArchiveName.tar.gz file1/directory1 ...
tar cvjf ArchiveName.tar.bz2 file1/directory1 ...
tar cvJf ArchiveName.tar.xz file1/directory1 ...
zip AcrhiveName.zip file1 ...
zip -r AcrhiveName.zip directory1 ...
7z a ArchiveName.7z file1/directory1 ...

xz має найбільше стиснення.

Якщо в bzip2, gzip чи xz не задати імя файлу то вони працюють з стандартним вводом/виводом.

gzip не підходить для файлу розміром > 4 гб.

bzip2, gzip and xz options:
-1 ... -9 - set the compression level. -1 - fast compression. -9 - best compression.
Compression levels for xz are -0 ... -9. -0 - fast compression. -9 - best compression.
-c - write output on standard output; keep original files unchanged.
-d - decompress.
-k - keep (don't delete) input files during compression or decompression.
-T 0 - use all processor cores during compression by xz.
-T number - use specified number of processor cores during compression by xz.
-t - test. Check the compressed file integrity.
-v - verbose mode. xz displays the progress.

Backup device to xz archive: dd if=DeviceFile status=progress | xz -0 -T 0 > ArchiveName.xz
Use -0 and -T 0 if need.
Restore device from xz archive: xz -dc ArchiveName.xz | dd of=DeviceFile status=progress

Backup device to bz2 archive: dd if=DeviceFile status=progress | bzip2 -1 > ArchiveName.bz2
Use -1 if need.
Restore device from bz2 archive: bzip2 -dc ArchiveName.bz2 | dd of=DeviceFile status=progress

Compress to bz2 archive and delete file: bzip2 FileName
Decompress and delete bzip2 archive: bzip2 -d ArchiveName.bz2

Compress to gz archive and delete file: gzip FileName
Decompress and delete gz archive: gzip -d ArchiveName.gz

Compress to xz archive and delete file: xz FileName

Decompress and delete xz archive:
xz -d ArchiveName.xz
unxz ArchiveName.xz

Decompress xz archive to stdout: xzcat ArchiveName.xz

7z використовує одночасно всі ядра процесору.

Compress standart input to 7z archive: command | 7z a -si ArchiveName
Extract 7z archive to standart output: 7z x -so ArchiveName

File split example: 7z a -v20m zombi.7z zombi.avi

Test zip archive: unzip -t AcrhiveName '*'
Test 7z archive: 7z t ArchiveName
Check the gz archive integrity: gzip -tv AcrhiveName
Check the bz2 archive integrity: bzip2 -tv AcrhiveName
Check the xz archive integrity: xz -tv AcrhiveName

List the content of a zip archive: zipinfo ArchiveName
List the content of a zip archive with one file per line showing: zipinfo -1 ArchiveName
List the content of a tar archive: tar tf ArchiveName
List the content of a 7z archive: 7z l ArchiveName
List the content of a rar archive: unrar l ArchiveName

Unpack zip archive to current directory: unzip ArchiveName
Unpack zip archive to specified directory: unzip ArchiveName -d DirectoryPath
Unpack tar.gz archive to current directory: tar xvzf ArchiveName.tar.gz
Unpack tar.bz2 archive to current directory: tar xvjf ArchiveName.tar.bz2
Unpack tar.xz archive to current directory: tar xvJf ArchiveName.tar.xz
Extract 7z archive to current directory: 7z e ArchiveName
Extract rar archive to current directory: unrar e ArchiveName

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                                             Processes

ps - report a snapshot of the current processes.
ps command samples:
ps -e
ps ax
ps axu
ps x
ps -eo args --sort args
ps axo args --sort args
ps -eo comm
ps -eo comm,user
ps -eo comm,%cpu --sort %cpu
ps -eo %cpu --no-headers  | tr -d ' ' | paste -s -d + | bc
ps -C Xvnc -o args ww
ps uU simple_user

Show information about process with pid 22470: ps 22470
Show detailed information about process with pid 22470: ps u 22470

-e, ax : list all processes.
x : list processes of current user.
-C cmdlist : select by command name.
-u userlist, U userlist : select by effective user ID (EUID) or name.

-f : full-format listing.
-F : extra full format.
-o, o : user-defined format.
u : display user-oriented format.
-w, w : wide output. Use this option twice for unlimited width.

pstree - display a tree of processes.
pidof - find the process ID of a running program.
Show working directory of a process with pid 8367: pwdx 8367
Find procceses which use the file: fuser -v file

list files opened by processes: lsof
List processes that opened a file: lsof file_path
List opened files of a process with pid 22470: lsof -p 22470

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                                                Users

Show users list: cut -d: -f1 < /etc/passwd
Print user identity: id

Add user: useradd user_name
Add user in Debian: adduser user_name
Add user and specify his home directory: useradd -d directory_path user_name
Add user and specify his home directory in Debian: adduser --home directory_path user_name

Delete user: userdel user_name
Delete user with his home directory: userdel -r user_name
Delete user in Debian: deluser user_name
Delete user with his home directory in Debian: deluser --remove-home user_name

Change user password: passwd user_name
Change current user password: passwd
Show password status: passwd -S user_name
Generate quality controllable random passphrase: pwqgen

Show groups list: cat /etc/group
Show user groups: groups user_name
Add user to group: gpasswd --add user_name group
Add user to administrator group: gpasswd --add user_name wheel
Delete user from group: gpasswd --delete user_name group
Add group: groupadd group_name
Delete group: groupdel group_name

Run a command from other user: sudo -u user_name command
Run a command from other user variant 2: su -c command user_name
Run shell from other user: su - user_name

users - print the names of users currently logged in to the current host.
lastlog - reports the most recent login of all users or of a given user.
Print the lastlog record of the specified user: lastlog -u user_name
last - show a listing of last logged in users.
Show 10 last logins (may be other numbrer): last -10

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                                               journalctl

journalctl - query the systemd journal.

Show messages about errors: journalctl -b -p err
Show messages about warnings and errors: journalctl -b -p warning
Show messages about notices, warnings and errors: journalctl -b -p notice
May also help on service error: journalctl -xe
journalctl --disk-usage

-b : show log from last boot.
-b -1 : show log of previous boot.
-n, --lines= : show the most recent journal events and limit the number of events shown.
-r : reverse output so that the newest entries are displayed first.
-f : show only the most recent journal entries, and continuously print new entries as they are appended to the journal.
-k : show only kernel messages.
--no-pager : do not pipe output into a pager.
-e, --pager-end : immediately jump to the end in the pager.
-x, --catalog : add message explanations where available.

-t, --identifier=SYSLOG_IDENTIFIER
           Show messages for the specified syslog identifier SYSLOG_IDENTIFIER.
Sample:
journalctl -t sshd

-u, --unit=UNIT|PATTERN
           Show messages for the specified systemd unit UNIT (such as a service unit), or for
           any of the units matched by PATTERN.

Samples:
journalctl _SYSTEMD_UNIT=vncserver.service
journalctl _PID=28097

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										rsync

rsync - versatile, remote and local file copying tool.

За замовчанням rsync не копіює файл якщо він вже існує в цільовій папці і має той самий розмір та час зміни.
Копіювати файл з індикатором прогресу: rsync --progress -h source destination
Для копіювання папки потрібна опція -r.
При опції -v (не потрібна при --progress) rsync буде пояснювати що він робить.

При копіюванні папки за замовчанням в destination створюється одноімена папка і файли копіюються в неї.
Щоб скопіювати файли з папки source в папку destination безпосередньо, потрібно після source вказати слеш.

-h                 показувати числа в зручному для людини стилі.
--list-only        list the files instead of copying them : показати список файлів замість копіювання.
-c, --checksum     skip based on checksum, not mod-time & size : пропуск буде оснований на контрольній сумі а не на часі зміни і розміру.
--size-only        skip files that match in size : пропускати копіювання якщо оригінал та цільовий файл має однаковий розмір.
-I, --ignore-times don't skip files that match size and time : не пропускати копіювання файлів.
--delete           delete extraneous files from dest dirs : видалити стороні файли з цільової папки.
-z, --compress     compress file data during the transfer.
--stats            показати підсумкову статистику після завершення.

--exclude=PATTERN  exclude files matching PATTERN.
PATTERN задається відносно source. Якщо напочатку PATTERN є /, цей символ вважається початком відносного шляху.
Замість шаблону можна вказати імя або відносний щлях файлу чи папки. Після папки потрібно вказати /.

-r, --recursive    recurse into directories.
-l, --links        copy symlinks as symlinks.
-t, --times        preserve modification times : зберігати час зміни файлів.
-p, --perms        preserve permissions.
-o, --owner        preserve owner (super-user only).
-g, --group        preserve group.

-------------------------------------------------------------------------------------------------
                                      systemctl and systemd

systemctl - Control the systemd system and service manager.

-a, --all
           When listing units with list-units, also show inactive units and units which are
           following other units. When showing unit/job/manager properties, show all
           properties regardless whether they are set or not.

-n, --lines=
           When used with status, controls the number of journal lines to show, counting from
           the most recent ones. Takes a positive integer argument. Defaults to 10.

--no-pager
           Do not pipe output into a pager.

List running units:
systemctl
systemctl --type=service

Show failed units: systemctl --failed

Show service status: systemctl status service_name
Help about unit: systemctl help unit_name

Kill all service processes: systemctl kill service_name

Start service: systemctl start service_name
Stop service: systemctl stop service_name

Enable service autostart: systemctl enable service_name
Disable service autostart: systemctl disable service_name

Block service start: systemctl mask service_name
Unblock service start: systemctl unmask service_name

A service file may be created in /etc/systemd/system directory.

Analyze startup time: systemd-analyze
Analyze services startup time: systemd-analyze blame

Get default mode: systemctl get-default
Set text mode (runlevel 3) as default: systemctl set-default multi-user.target
Set graphical mode (runlevel 5) as default: systemctl set-default graphical.target

--------------------------------------------------------------------------------------------------
												grub

Переустановити grub, якшо в системі є розділ boot, можна таким способом:

1) Завантажити лінукс з компакт диску або флешки.

2) Відкрити термінал і увійти в сеанс root командою
su -

3) Змонтувати розділ boot в якусь папку.

Якщо розділ boot це /dev/sda1 то змонтувати його в точку монтування /mnt/sda1 можна наприклад командами
mkdir /mnt/sda1
mount /dev/sda1 /mnt/sda1

Додаткові опції до mount не обовязкові. Тип файлової системи визначиться автоматично.

4) Виконати команду
grub2-install --boot-directory=точка_монтування_розділу_boot /dev/sda
/dev/sda це завантажувальний пристрій. Замість /dev/sda може бути інший пристрій.
Якщо --boot-directory не вказати, буде використовуватись папка /boot.

Приклад:
grub2-install --boot-directory=/mnt/sda1 /dev/sda

5) Переналаштувати grub командою
grub2-mkconfig -o точка_монтування_розділу_boot/grub2/grub.cfg

Приклад:
grub2-mkconfig -o /mnt/sda1/grub2/grub.cfg

6) Перезавантажити компютер. Вибрати правильний варіант завантаження.
Правильний варіант може бути наприклад Fedora (on /dev/sda2).
/dev/sda2 це розділ для прикладу куди була встановлена Fedora, її кореневий розділ.

7) Після успішного завантаження переналаштувати grub командою
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

----------------------------------------------

Якщо в системі немає розділу boot, переустановити grub можна таким способом:

1) Завантажити лінукс з компакт диску або флешки.

2) Відкрити термінал і увійти в сеанс root командою
su -

3) Змонтувати кореневий розділ в якусь папку.

4) Виконати команду
grub2-install --boot-directory=точка_монтування_кореневого_розділу/boot /dev/sda
/dev/sda це завантажувальний пристрій. Замість /dev/sda може бути інший пристрій.

Приклад 1:
grub2-install --boot-directory=/mnt/sda1/boot /dev/sda

Приклад 2:
grub2-install --boot-directory=/run/media/liveuser/root/boot /dev/sdb

5) Переналаштувати grub командою
grub2-mkconfig -o точка_монтування_кореневого_розділу/boot/grub2/grub.cfg

Приклад 1:
grub2-mkconfig -o /mnt/sda1/boot/grub2/grub.cfg

Приклад 2:
grub2-mkconfig -o /run/media/liveuser/root/boot/grub2/grub.cfg

Виконати пункти 6 та 7 з попереднього розділу.

----------------------------------------------

Переналаштувати grub: grub2-mkconfig -o /boot/grub2/grub.cfg
Документація про grub: info grub2
Файл /etc/default/grub визначає те як grub буде налаштовуватись.

Приклад файлу /etc/default/grub:
GRUB_TIMEOUT=2
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rhgb quiet"
GRUB_DISABLE_OS_PROBER=true
GRUB_DISABLE_RECOVERY=true

--------------------------------------------------------------------------------------------------
			                                SELinux

chcon - change file SELinux security context.
Show SELinux alerts: sudo sealert -a /var/log/audit/audit.log
Clear SELinux log: echo -n "" > /var/log/audit/audit.log
Show policies list: semodule --list=full
Remove policy: semodule -r policy_name
Relabel file system: touch /.autorelabel; reboot

--------------------------------------------------------------------------------------------------
                              	  Devices

Show data about computer: sudo lshw | less
Show short data about computer: sudo lshw -short
Save data about computer in html file: sudo lshw -html > file_name
Show data about motherboard and other devices: sudo lshw -class bus
Show data about videocard: sudo lshw -class display
sudo lshw -class processor
Show data about operational memory: free -m
                                    free -h
Show /dev/sda partitions list: sudo parted /dev/sda print
Show /dev/sda partitions list with free space: sudo parted /dev/sda print free

Check webcam:
mplayer tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0:fps=30
mplayer tv:// device=/dev/video0

Monitor devices connecting and disconnecting: udevadm monitor
Monitor devices connecting and disconnecting, show properties: udevadm monitor -p

Show device info:
udevadm info device_file
udevadm info -a device_file

sudo fdisk -l [device]
List the partition tables for the specified devices and then exit.
If no devices are given, those mentioned in /proc/partitions (if that file exists) are used.

Display a list of mounted file systems: findmnt

Get partition label, UUID and file system type: sudo blkid [device]
If no device are given, all partitions will be shown.

lsblk [options] [device ...]
List information about block devices.

lsblk -f
List storage devices, their fs types, labels, UUIDs, mount points.

lsblk -f -o +SIZE
List storage devices, their fs types, labels, UUIDs, mount points, sizes.

lsblk -o +FSUSED,LABEL
List storage devices, include their used sizes and labels.

lsblk -o NAME,TYPE,SIZE,FSUSED,LABEL,MOUNTPOINT
Sample of storage devices list.

Show information about SSD:
smartctl -i device
smartctl -a device

Show SSD SMART attributes: smartctl -A device

Show information about disks:
lshw -class disk
hwinfo --disk

dmidecode - DMI table decoder.
An information about motherboard, processor and other devices may be get by dmidecode.

lscpu - display information about the processor.
lsmem - list the ranges of available memory with their online status.
lspci - list PCI devices. An information about videocard may be get by lspci.
List USB devices: lsusb

Build the nvidia kernel module: sudo akmods

Set sound card profile: pactl set-card-profile card profile

List sound cards:
pactl list cards
pactl list short cards
pactl list sinks
pactl list short sinks
aplay -l

List PCMs: aplay -L

Play file: aplay file_name
Play file to specified PCM: aplay -D PCM_name file_name

List power sources: upower -e
Show power source state: upower -i power_source_path

Detect sensors: sudo sensors-detect
sensors - print sensors information.
Monitor sensors: watch -t sensors -A

Show kernel parameters: cat /proc/cmdline

List input devices: xinput --list
List input device properties: xinput --list-props device_id_or_name

Slow doun mouse:
xinput --set-prop device_id_or_name 'Coordinate Transformation Matrix' 0.7 0 0 0 0.7 0 0 0 1

List available bluetooth adapters: bt-adapter -l
Show information about bluetooth adapter: bt-adapter -i
Discover remote bluetooth devices: bt-adapter -d

List bluetooth devices: bt-device -l
Show information about bluetooth device: bt-device -i <name|mac>
Connect to the bluetooth device and initiate the pairing: bt-device -c <mac>
Disconnect bluetooth device: bt-device -d <name|mac>
Remove bluetooth device: bt-device -r <name|mac>

Control bluetooth device: bluetoothctl

-----------------------------------------------------------------------------------
						bluetoothctl commands

List available controllers: list
Controller information: show [controler]
Scan for devices: scan on
List available devices: devices
List paired devices: paired-devices
Device information: info <device>
Remove device: remove <device>
Disconnect device: disconnect [device]

Connect device:
	trust <device>
	pair <device>
	connect <device>

--------------------------------------------------------------------------------------------------
                                             Kernel modules

List kernel modules:
find /lib/modules/$(uname -r) -name '*.ko*'

List loaded kernel modules: lsmod
Show module info: modinfo module_name
Load module: modprobe module_name
Load module from file: insmod file_name [args]
Unload module: modprobe -r module_name
Unload module, alternative variant: rmmod module_name

Loaded modules may be found in /sys/module.
Modules marameters values may be found in /sys/module/module_name/parameters.

--------------------------------------------------------------------------------------------------
                                 Important grep options

Regexp selection and interpretation:
  -E, --extended-regexp     PATTERN is an extended regular expression
  -F, --fixed-strings       PATTERN is a set of newline-separated strings
  -i, --ignore-case         ignore case distinctions
  -w, --word-regexp         force PATTERN to match only whole words
  -x, --line-regexp         force PATTERN to match only whole lines
  -v, --invert-match        select non-matching lines

Output control:
  -m, --max-count=NUM       stop after NUM matches
  -b, --byte-offset         print the byte offset with output lines
  -n, --line-number         print line number with output lines
  -H, --with-filename       print the file name for each match
  -h, --no-filename         suppress the file name prefix on output
  -o, --only-matching       show only the part of a line matching PATTERN
  -q, --quiet, --silent     suppress all normal output
  -d, --directories=ACTION  how to handle directories;
                            ACTION is 'read', 'recurse', or 'skip'
  -r, --recursive           like --directories=recurse
  -R, --dereference-recursive
                            likewise, but follow all symlinks
      --include=FILE_PATTERN
                            search only files that match FILE_PATTERN
      --exclude=FILE_PATTERN
                            skip files and directories matching FILE_PATTERN
        --exclude-dir=PATTERN directories that match PATTERN will be skipped.
  -L, --files-without-match print only names of FILEs containing no match
  -l, --files-with-matches  print only names of FILEs containing matches
  -c, --count               print only a count of matching lines per FILE

Context control:
  -B, --before-context=NUM  print NUM lines of leading context
  -A, --after-context=NUM   print NUM lines of trailing context
  -C, --context=NUM         print NUM lines of output context
  -NUM                      same as --context=NUM
      --group-separator=SEP use SEP as a group separator
      --no-group-separator  use empty string as a group separator

-------------------------------------------------------------------------------
                             git commands

git apply ctools-1444006-disallowed-unicode-code-point-18.patch
git config --global user.name 'Sergiy Vovk'
git config --global user.email grayvovk@meta.ua
git config --list
git init
git add testscript.php
git add .
Commit: git commit -m 'Message.'
Change message of last commit: git commit --amend -m 'Message.'
Restore testscript.php from last commit: git checkout -- testscript.php
git log
git log --pretty=oneline
git clone git://github.com/schacon/grit.git
git remote add pb git://github.com/paulboone/ticgit.git
git remote rm pb
git remote
git remote -v
git fetch pb
git pull
git push
git push origin master
git tag - tags list.
git tag v1.4 - add v1.4 tag to the last commit.
git tag -a v1.4 -m 'version 1.4'
git show v1.4 - show v1.4 tag data.
git branch testing - create testing branch.
git checkout testing - select testing branch.
git checkout -b testing - create testing branch and select it.
git branch -d testing - delete testing branch.
git branch - branches list.
git branch -v - branches and last commits list.
git branch --merged - list merged branches.
git merge testing - merge testing branch to current branch.
View remote url: git remote -v
Change the origin remote url: git remote set-url origin https://github.com/user/repo.git

------------------------------------------------------------------------------------------
                                             ip

ip - show / manipulate routing, network devices, interfaces and tunnels

Network device configuration: ip link [command]

List network interfaces: ip link
List up network interfaces: ip link show up

Show network interfaces statistic: ip -s -h link
Show wlp3s0 interface statistic: ip -s -h link show wlp3s0
Show wlp3s0 interface attributes: ip link show wlp3s0

Set enp2s0 interface up: sudo ip link set enp2s0 up
Set enp2s0 interface down: sudo ip link set enp2s0 down

------------------------------------------------------------------------------------------
                                        nmcli and PPPoE
nmcli - command-line tool for controlling NetworkManager.

Show status for all network devices: nmcli device
Show information about all network devices: nmcli device show
Show information about wlp3s0 network device: nmcli device show wlp3s0
Show wifi access points status: nmcli device wifi
Connect to wifi access point MyHomeNet: nmcli device wifi connect MyHomeNet
Connect to wifi access point MyHomeNet with password prompt: nmcli --ask device wifi connect MyHomeNet
List network connection: mcli connection
Show MyHomeNet connection information: mcli connection show MyHomeNet

Встановити пакунки для PPPoE: sudo dnf -y install ppp rp-pppoe net-tools initscripts
Налаштувати PPPoE: sudo pppoe-setup
Підняти підключення PPPoE: sudo ifup ppp0

-------------------------------------------------------------------------------------------
                                  Work with MySQL database

Change MySQL password for root user: mysqladmin -u root password 365abc
mysql -u vovk -p369 shop
Show databases list: mysqlshow -u root -p
Show tables list: mysqlshow -u user_name -p database_name
Команда для імпорту файлу sql в базу даних: mysql -u user_name -p database_name < sql_file_name
Команда для імпорту файлу gz в базу даних: gunzip -c gz_file_name|mysql -u user_name -p database_name
Команда для експорту бази даних в файл: mysqldump -u user_name -p database_name > sql_file_name
-h host_name : connect to the MySQL server on the given host.

--------------------------------------------------------------------------------

Запустити qmmp о 21:00 сьогодні: echo 'DISPLAY=:0 qmmp' | at 21:00 today
Запустити qmmp о 21:00 завтра: echo 'DISPLAY=:0 qmmp' | at 21:00 tomorrow
Запустити qmmp через 5 хвилин: echo 'DISPLAY=:0 qmmp' | at now + 5 minutes
Запустити qmmp через 5 годин: echo 'DISPLAY=:0 qmmp' | at now + 5 hours
Вивести список призначених завдань: atq
Вивести команду для призначеного завдання: at -c номер
Видалити призначене завдання: atrm номер
DISPLAY=:0 потрібна для графічної програми.

--------------------------------------------------------------------------------

The cron fields:
              field          allowed values
              -----          --------------
              minute         0-59
              hour           0-23
              day of month   1-31
              month          1-12 (or names)
              day of week    0-7 (0 or 7 is Sun, or use names)
              command

Task install example:
echo '0 12 * * 2,4 /home/taras/Scripts/UpdateApartmentDatabase.sh' | crontab -
Note: the old tasks will be removed.

Run /root/vsystemchecker every 30 minute:
*/30 * * * * /root/vsystemchecker > /var/log/vsystemchecker.log

List tasks of current user: crontab -l
List tasks of taras user: crontab -u taras -l
Edit tasks: crontab -e
Remove task: crontab -r

--------------------------------------------------------------
				dnf and rpm commands

Get upgrades list for installed packages: dnf list upgrades
List packages from repo: dnf repository-packages repo_name list --all

List orphaned packages: rpmorphan --all
List unused packages: dnf list autoremove
Remove unused packages: dnf autoremove

Add repo file to dnf configuration: dnf config-manager --add-repo repo_file
The repo_file may be also in internet.

Get installed packages list:
rpm -qa | sort
rpm -qa --queryformat '%{NAME}\n' | sort
rpm -qa --queryformat '%{NAME}: %{SUMMARY}\n' | sort

Get package files list:
dnf repoquery -l package_name
rpm -ql package_name
rpm -qlp package_file

Get package information:
rpm -qi package_name
rpm -qip package_file

Get package name of file:
dnf provide patern
dnf repoquery --file file
rpm -qf file

Verify package: rpm -V package_name
Install package: rpm -ihv package_file

--------------------------------------------------------------
				btrfs commands

Format partition to btrfs file system:
sudo mkfs.btrfs -L label -f device

Check btrfs file system: sudo btrfs check device
Check btrfs file system, verify data checksums: sudo btrfs check --check-data-csum -p device
-p: show progress.

Check data integrity on btrfs filesystem, repair danaged data
if posible:
sudo btrfs scrub start -B device_or_path
Other way:
sudo btrfs scrub start device_or_path
sudo btrfs scrub status device_or_path

Repair btrfs file system: sudo btrfs check --repair device

Show information about filesystem usage: btrfs filesystem usage partition-mount-point
Show short information about filesystem: btrfs filesystem df partition-mount-point

Show information about filesystem: sudo btrfs filesystem show device
If device is not specified, information about all btrfs filesystems is shown.

Show label: btrfs filesystem label device-or-mountpoint
Set label: sudo btrfs filesystem label device-or-mountpoint new-label

Defragment filesystem: sudo btrfs filesystem defragment -v -r directory
If the filesystem has more than 1 subvolumes,
each subvolume should be defragmented separately.

Save subvolume to file: sudo btrfs send -f file subvolume-path
Restore subvolume from file: sudo btrfs receive -f file partition-mount-point

List subvolumes: sudo btrfs subvolume list partition-mount-point
Create subvolume: sudo btrfs subvolume create partition-mount-point/subvolume-name

Create subvolume snapshot: sudo btrfs subvolume snapshot subvolume-path snapshot-path
Create subvolume readonly snapshot:
sudo btrfs subvolume snapshot -r subvolume-path snapshot-path
A subvolume may be copied by btrfs subvolume snapshot command.
A usual subvolume may be created from readonly
subvolume by btrfs subvolume snapshot command.

Delete subvolume: sudo btrfs subvolume delete partition-mount-point/subvolume-name
Rename subvolume: sudo mv path new-path

Show information about subvolume:
sudo btrfs subvolume show partition-mount-point/subvolume-name

--------------------------------------------------------------
				snap commands

List installed snaps: snap list
Find snap: snap find text
Get snap info: snap info snap_name
Run snap: snap run snap_name
Install snap: sudo snap install snap_name
Remove snap: sudo snap remove snap_name
Update snap: sudo snap refresh snap_name
Update all snaps: sudo snap refresh

--------------------------------------------------------------

				CentOS commands

Enable auto load of httpd service:
chkconfig httpd on
chkconfig --level 2 httpd off

Disable auto load of httpd service: chkconfig httpd off
Show auto load status of httpd service: chkconfig --list httpd
Show auto load status of all services: chkconfig --list

--------------------------------------------------------------

				Ubuntu and Debiam commands

service - run a System V init script
Sample: service vsftpd status
List services and its statuses: service --status-all
initctl list - services list.
Reload nginx server: service nginx reload
Restart ssh server: service ssh restart

Update packages database: apt update
Update all packages in Ubuntu: apt upgrade
Update all packages in Debian: aptitude safe-upgrade
List packages: apt list [pattern]
Show information about package: apt show package_name
Find package: aptitude search string
Find package by file name: dpkg -S file_name
List packages matching given pattern: dpkg -l package-name-pattern
Report status of specified package: dpkg -s package-name
List package files: dpkg -L package_name

Install package from file: dpkg -i file_name
install missing dependicies: apt-get -f install

Install or update package: apt install package_name
Reinstall package: apt install --reinstall package_name
Remove package: apt remove package_name
Show holded packages list: dpkg --get-selections | grep hold
Disable package update: echo 'package_name hold' | dpkg --set-selections
Enable package update: echo 'package_name install' | dpkg --set-selections
Find package by file path: apt-file search file_path