Comparison table of popular Linux distributions#

Some questions worth thinking about before deciding on a distribution include#

• What is the main function of the system (server or desktop)?
• What types of packages are important to the organization? For example, web server, word processing, etc.
• How much storage space is required, and how much is available? For example, when installing Linux on an embedded device, space is usually constrained.
• How often are packages updated?
• How long is the support cycle for each release? For example, LTS releases have long-term support.
• Do you need kernel customization from the vendor or a third party?
• What hardware are you running on? For example, it might be X86, RISC-V, ARM, PPC, etc.
• Do you need long-term stability? Or can you accept (or need) a more volatile cutting-edge system running the latest software versions?

Release model: Rolling releases và Fixed release#

Khi chọn distro Linux, một trong những khác biệt quan trọng nhất là mô hình phát hành (release model).
Nó quyết định việc update có “sướng” hay “đau”, và hệ thống ổn định đến mức nào.

1
pacman -Syu

Package Management Systems on Linux#

There are two broad families of package managers widely deployed: those based on Debian and those which use RPM as their low-level package manager. The two systems are incompatible but, broadly speaking, provide the same essential features and satisfy the same needs. In addition, there are some other systems used by more specialized Linux distributions.

Both package management systems operate on two distinct levels: a low-level tool (such as dpkg or rpm) takes care of the details of unpacking individual packages, running scripts, getting the software installed correctly, while a high-level tool (such as apt, dnf, or zypper) works with groups of packages, downloads packages from the vendor, and figures out dependencies.

Most of the time users need to work only with the high-level tool, which will take care of calling the low-level tool as needed. Dependency resolution is a particularly important feature of the high-level tool, as it handles the details of finding and installing each dependency for you. Be careful, however, as installing a single package could result in many dozens or even hundreds of dependent packages being installed.

Cre: The Linux Foundation - Linux Foundation X LFS101: Introduction to Linux

Working With Different Package Management Systems#

The Advanced Packaging Tool (apt) is the underlying package management system that manages software on Debian-based systems. While it forms the backend for graphical package managers, such as the Ubuntu Software Center and synaptic, its native user interface is at the command line, with programs that include apt (or apt-get) and apt-cache.

dnf is the open source command-line package-management utility for the RPM-compatible Linux systems that belong to the Red Hat family.

zypper is the package management system for the SUSE/openSUSE family and is also based on RPM. zypper also allows you to manage repositories from the command line. zypper is fairly straightforward to use and closely resembles dnf.

• Table: Basic Packaging Commands

Cre: The Linux Foundation - Linux Foundation X LFS101: Introduction to Linux

Navigating the File System#

Relative path vs Absolute path

• Relative path: path from current directory

  • ./file.txt : current directory

  • ../file.txt : parent directory

• Absolute path: full path from root directory

  • /home/user/file.txt
  • //var/log/syslog: even with double slash at the beginning, it’s still absolute path

cd: Change directory

• cd /home/user

• cd ~

• cd ..

  im using zoxide: better cd

ls: List files and directories

• ls
• ls -l | ls -al
• ls -a
• ls -lt : sort time descending
• ls -ltr: sort time ascending (r = reverse)

im using exa: better ls

pw : print current working directory

Viewing Files#

1
cat <filename>

1
$ cat << EOF > myfile
2
> line one
3
> line two
4
> line three
5
> EOF
6
$

touch#

$ touch <filename> This is normally done to create an empty file as a placeholder for a later purpose.

touch provides several useful options. For example, the -t option allows you to set the date and timestamp of the file to a specific value, as in:

$ touch -t 202201011200.00 newfile.txt

This command creates a new file named newfile.txt with a timestamp of January 1, 2022, at 12:00 PM.

Moving, Copying, Deleting Files and Directories#

mkdir : Create a directories

• mkdir hihi: create directory hihi in current directory
• mkdir /usr/share/hihi: create directory hihi in /usr/share
• mkdir /hihi/hehe/huhu => No such file or directory => mkdir -p /hihi/hehe/huhu ok

• Because normal mkdir only support one directory, if pass parent/child/… it cause error -> using -p (parent) to fix

rmdir

Removing a directory is done with rmdir. The directory must be empty or the command will fail. To remove a directory and all of its contents you have to do rm -rf.

rm : Remove files and directories

• rm file.txt
• rm -r dir1: Remove directory recursively
• rm -rf dir1: Remove directory with force and recursively

cp : Copy files and directories

• cp file.txt file2.txt
• cp -r dir1 dir2
• cp * /usr/share/.fonts

mv : Move files and directories

• mv file.txt /usr/share/.fonts

• mv file.txt file2.txt

• mv * /usr/share/.fonts

• we can perform the rename file or directory by mv command: if i want to rename the file demo.txt to test.txt

  1
  mv demo.txt test.txt
  2
  # same as directory
  

echo : Write text to file

• echo "Hello World" > file.txt
• echo “alias ‘yt=ytfzf -t’” >> ~/.bashrc
• echo “alias ‘ll=ls -al’” >> ~/.bashrc
• echo “alias ‘showdisk=cd /media/lcaohoanq/ ; ls -al’” >> ~/.bashrc

nano : Text editor

• nano file.txt

unzip : Unzip files

• unzip file.zip

tree : Show the current directory with the tree visualization

1
# show everything
2
tree
3

4
# show directories only
5
tree -D
6

7
# show directories except the pattern
8
tree -I "node_modules"
9

10
# show except the pattern, directories only
11
tree -I "node_modules" -D

history: Show all previously executed command

• !!: execute the last command again (bang bang)
• !n: execute the nth command in history
• !string: execute the last command that starts with string
• Ctrl + r: reverse search in history

im currently using atuin: better history, with built in sql lite, can search, navigate to the previous command

• Process:

  • ps: shows only processes associated with your current terminal session and use

  • ps aux: display a detailed snapshot of all running processes on the system

    1
    # show detailed all running processes and find obs
    2
    ps aux | grep "obs"
    

Terminal Shortcuts#

find : Search for files and directories#

find is an extremely useful and often-used utility program in the daily life of a Linux system administrator. It recurses down the filesystem tree from any particular directory (or set of directories) and locates files that match specified conditions. The default pathname is always the present working directory.

-name: list files with certain pattern in their name -iname: case insensitive version of -name -type: search by file type (f: regular file, d: directory, l: symbolic link, c: character device, b: block device) -size: search by file size (+: greater than, -: less than, no sign: exactly) -ctime: search by change time (in days, +: more than, -: less than, no sign: exactly) -atime: search by access time (in days, +: more than, -: less than, no sign: exactly) -mtime: search by modification time (in days, +: more than, -: less than, no sign: exactly)

System Information#

• Check CPU:

  • nproc
  • lscpu

• Check RAM

  • free -h
  • cat /proc/meminfo

• Check Disk:

  • df -h: disk free

  1
  ❯ df -h
  2
  Filesystem      Size  Used Avail Use% Mounted on
  3
  udev             16G     0   16G   0% /dev
  4
  tmpfs           3.2G  2.1M  3.2G   1% /run
  5
  /dev/sdb1       208G   88G  111G  45% /
  6
  tmpfs            16G   91M   16G   1% /dev/shm
  7
  tmpfs           5.0M  8.0K  5.0M   1% /run/lock
  8
  tmpfs           1.0M     0  1.0M   0% /run/credentials/systemd-journald.service
  9
  tmpfs            16G   15M   16G   1% /tmp
  10
  /dev/nvme0n1p1  234G  155G   68G  70% /media/data
  11
  tmpfs           3.2G  148K  3.2G   1% /run/user/1000
  

  • lsblk: list block devices

  1
  ❯ lsblk
  2
  NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
  3
  sda           8:0    0 931.5G  0 disk
  4
  ├─sda1        8:1    0 496.7G  0 part
  5
  └─sda2        8:2    0 434.9G  0 part
  6
  sdb           8:16   0 223.6G  0 disk
  7
  ├─sdb1        8:17   0 212.2G  0 part /
  8
  ├─sdb2        8:18   0     1K  0 part
  9
  └─sdb5        8:21   0  11.4G  0 part [SWAP]
  10
  nvme0n1     259:0    0 238.5G  0 disk
  11
  └─nvme0n1p1 259:1    0 238.5G  0 part /media/data
  

  • -a: all devices

  1
  ❯ lsblk -a
  2
  NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
  3
  sda           8:0    0 931.5G  0 disk
  4
  ├─sda1        8:1    0 496.7G  0 part
  5
  └─sda2        8:2    0 434.9G  0 part
  6
  sdb           8:16   0 223.6G  0 disk
  7
  ├─sdb1        8:17   0 212.2G  0 part /
  8
  ├─sdb2        8:18   0     1K  0 part
  9
  └─sdb5        8:21   0  11.4G  0 part [SWAP]
  10
  nvme0n1     259:0    0 238.5G  0 disk
  11
  └─nvme0n1p1 259:1    0 238.5G  0 part /media/data
  

  • -o: specify output columns (check all column lsblk --list-columns)

  1
  ❯ lsblk -a -o NAME,SIZE,FSTYPE,UUID,MOUNTPOINT
  2
  NAME          SIZE FSTYPE UUID                                 MOUNTPOINT
  3
  sda         931.5G
  4
  ├─sda1      496.7G ntfs   01D819C87037D350
  5
  └─sda2      434.9G ntfs   01D819C871BA0680
  6
  sdb         223.6G
  7
  ├─sdb1      212.2G ext4   2c9bf3d9-8c80-4d4d-8632-4b10e65726d3 /
  8
  ├─sdb2          1K
  9
  └─sdb5       11.4G swap   9eacdd7d-3177-4e92-a812-63e0abaade65 [SWAP]
  10
  nvme0n1     238.5G
  11
  └─nvme0n1p1 238.5G ext4   26a0de97-0abd-45e1-b610-129d3045f430 /media/data
  

  • fdisk: older systems or simple MBR tasks

  1
  ❯ sudo fdisk -l
  2
  Disk /dev/nvme0n1: 238.47 GiB, 256060514304 bytes, 500118192 sectors
  3
  Disk model: INTEL SSDPEKKF256G8L
  4
  Units: sectors of 1 * 512 = 512 bytes
  5
  Sector size (logical/physical): 512 bytes / 512 bytes
  6
  I/O size (minimum/optimal): 512 bytes / 512 bytes
  7
  Disklabel type: gpt
  8
  Disk identifier: 677D2B55-C4FB-4DB8-BEC3-AAADCE78C24A
  9
  
  10
  Device         Start       End   Sectors   Size Type
  11
  /dev/nvme0n1p1  2048 500117503 500115456 238.5G Linux filesystem
  12
  
  13
  
  14
  Disk /dev/sdb: 223.57 GiB, 240057409536 bytes, 468862128 sectors
  15
  Disk model: KINGSTON SA400S3
  16
  Units: sectors of 1 * 512 = 512 bytes
  17
  Sector size (logical/physical): 512 bytes / 512 bytes
  18
  I/O size (minimum/optimal): 512 bytes / 512 bytes
  19
  Disklabel type: dos
  20
  Disk identifier: 0xf6b8904f
  21
  
  22
  Device     Boot     Start       End   Sectors   Size Id Type
  23
  /dev/sdb1  *         2048 445042687 445040640 212.2G 83 Linux
  24
  /dev/sdb2       445044734 468860927  23816194  11.4G  f W95 Ext'd (LBA)
  25
  /dev/sdb5       445044736 468860927  23816192  11.4G 82 Linux swap / Solaris
  26
  
  27
  
  28
  Disk /dev/sda: 931.51 GiB, 1000204886016 bytes, 1953525168 sectors
  29
  Disk model: TOSHIBA MQ04ABF1
  30
  Units: sectors of 1 * 512 = 512 bytes
  31
  Sector size (logical/physical): 512 bytes / 4096 bytes
  32
  I/O size (minimum/optimal): 4096 bytes / 4096 bytes
  33
  Disklabel type: gpt
  34
  Disk identifier: FEDF6762-A8BC-4D15-9D71-AFB6E5CDEA90
  35
  
  36
  Device          Start        End    Sectors   Size Type
  37
  /dev/sda1        2048 1041569791 1041567744 496.7G Microsoft basic data
  38
  /dev/sda2  1041569792 1953523119  911953328 434.9G Microsoft basic data
  

  • parted: newer systems or GPT tasks (or gdisk)

  1
  ❯ sudo parted -l
  2
  Model: ATA TOSHIBA MQ04ABF1 (scsi)
  3
  Disk /dev/sda: 1000GB
  4
  Sector size (logical/physical): 512B/4096B
  5
  Partition Table: gpt
  6
  Disk Flags:
  7
  
  8
  Number  Start   End     Size   File system  Name                  Flags
  9
  1      1049kB  533GB   533GB  ntfs         Basic data partition  msftdata
  10
  2      533GB   1000GB  467GB  ntfs         Basic data partition  msftdata
  11
  
  12
  
  13
  Model: ATA KINGSTON SA400S3 (scsi)
  14
  Disk /dev/sdb: 240GB
  15
  Sector size (logical/physical): 512B/512B
  16
  Partition Table: msdos
  17
  Disk Flags:
  18
  
  19
  Number  Start   End    Size    Type      File system     Flags
  20
  1      1049kB  228GB  228GB   primary   ext4            boot
  21
  2      228GB   240GB  12.2GB  extended                  lba
  22
  5      228GB   240GB  12.2GB  logical   linux-swap(v1)  swap
  23
  
  24
  
  25
  Model: INTEL SSDPEKKF256G8L (nvme)
  26
  Disk /dev/nvme0n1: 256GB
  27
  Sector size (logical/physical): 512B/512B
  28
  Partition Table: gpt
  29
  Disk Flags:
  30
  
  31
  Number  Start   End    Size   File system  Name                  Flags
  32
  1      1049kB  256GB  256GB  ext4         Basic data partition
  

• Disk usage:

  • du -h —max-depth=1: check current directory disk usage

  • du -sh /: check root directory disk usage summary

  • dust: better way to check disk usage than du, extremely fast

    1
    # check root directory
    2
    dust /
    

  • ncdu: TUI using ncurses, find exactly what’s taking space and want to clean up interactively

    1
    ncdu /
    

• Process management

  • top: mandatory tool

im using htop, btop, better UI, more efficient to do process management

• Power Management
  • sudo reboot: reboot system immediately
  • sudo shutdown -h: shutdown after 1 min
  • sudo shutdown -h now: shutdown immediately
  • sudo shutdown -P +10: schedule shutdown after 10 mins

Not mandatory command, but im using too many time

• Copy all content of file into clipboard

  • xclip way, make sure you installed xclip with sudo apt install xclip

  1
  cat <filename> | xclip -selection clipboard
  

Documentation and Manual Pages#

The man pages are the most often-used source of Linux documentation. They provide in-depth documentation about many programs and utilities, as well as other topics, including configuration files and programming APIs for system calls, library routines, and the kernel. They are present on all Linux distributions and are always at your fingertips.

• $ man <command>
  Open the official manual page for a command, including its description, options, and usage examples.

• $ man -f <command>
  Display a short list of manual pages related to the keyword (same as whatis), with brief descriptions.

• $ man -a <command>
  Show all available manual pages matching the command name, going through every section instead of just the first one.

Tips to remember#

• /etc → config

• /var → always change (log, cache)

• /proc & /sys → not a real file

• /usr → app + lib

• /bin vs /sbin → user vs admin

• /dev → everything is file 😎 (i want fine also)

File Ownership#

In Linux and other UNIX-based operating systems, every file is associated with a user who is the owner. Every file is also associated with a group (a subset of all users) which has an interest in the file and certain rights, or permissions: read, write, and execute.

File Permission Mods and chmod#

Every file have permission for owner and group (I tell file here but same for directory, link, socket,…)

• Owner is who created the file or directory
• Groups is the set of users who share the same permission

Files have three kinds of permissions: read (r), write (w), execute (x). These are generally represented as in rwx. These permissions affect three groups of owners: user/owner (u), group (g), and others (o)

1
rwx: rwx: rwx
2
 u:   g:   o

Example:

-rw-r--r--:

• owner user: can read, write, not execute (for each file the owner is root, oracle9, user3)
• group user: can read only
• other user: can read only

change file permissions

1
chmod [u/g/o][+/-/=][r/w/x][file]

Syntax:

• u/g/o: user/group/other
• +/-/=: add, remove, set
• r/w/x: read, write, execute

Examples:

• Change file data.txt add groups permission writable

1
chmod g+w data.txt

• Give the owner and others execute permission and remove the group write permission

1
$ ls -l somefile
2
-rw-rw-r-- 1 student student 1601 Mar 9 15:04 somefile
3
$ chmod uo+x,g-w somefile
4
$ ls -l somefile
5
-rwxr--r-x 1 student student 1601 Mar 9 15:04 somefile

1
chmod 664 foo.txt
2
# user/owner: read, group: read/write, other: read
3
# =>>>>>> rw-rw-r--
4
chmod 755 script.sh
5
# user/owner: read/write/execute, group: read/execute, other: read/execute
6
# =>>>>>> rwxr-xr-x

Chown command#

chown can change owner, group or both of a file or directory.

Touch 2 file file1 and file2 as owner is coop, group is coop, Change file2 owner to root remain group coop, after that change both owner and group of file? mean both to root
Finally, only the superuser can remove the files.

Syntax:

1
chown x:y file.txt

• x: user (owner)
• y: group

Some cases:

1
chown hoang:dev file.txt

• Change owner to hoang, group to dev

1
chown hoang file.txt

• Change owner to hoang, remain group

1
chown :dev file.txt

• Change group to dev, remain owner

1
chown -R hoang:dev /var/www

• Change owner to hoang, group to dev recursively for all files and directories in /var/www

Why change recursively? Because /var/www usually contain many files and directories, if we don’t use -R option, only /var/www change owner and group, all files and directories inside remain the same. Linux do this because it protect us from making mistakes. Ensure we really want to apply changes to all files and directories inside.

So always be careful:

1
chown -R user:group /

=> Disaster, because it change all files and directories in the system to user:group, system break down, need to reinstall

Chgrp command#

chgrp is used to change the group ownership of a file or directory.

1
chgrp dev file.txt

• Change group of file.txt to dev, remain owner
• Only the superuser or the owner of the file can change the group ownership.

Identifying the Current User#

As you know, Linux is a multi-user operating system, meaning more than one user can log on at the same time.

• To identify the current user, type whoami.
• To list the currently logged-on users, type who.

Giving who the -a option will give more detailed information.

1
hoang@fptu-thitkho-cbbz:~$ whoami
2
hoang
3
hoang@fptu-thitkho-cbbz:~$ who
4
hoang    pts/0        2026-01-22 21:49 (14.187.108.34)
5
hoang    pts/1        2026-01-21 15:52 (tmux(36912).%0)
6
minh     pts/2        2026-01-22 21:49 (14.187.108.34)
7
hoang@fptu-thitkho-cbbz:~$ who -a
8
           system boot  2026-01-21 11:09
9
           run-level 5  2026-01-21 11:09
10
LOGIN      ttyS0        2026-01-21 11:09               653 id=tyS0
11
LOGIN      tty1         2026-01-21 11:09               652 id=tty1
12
hoang    + pts/0        2026-01-22 21:49   .         37921 (14.187.108.34)
13
hoang    + pts/1        2026-01-21 15:52  old        36912 (tmux(36912).%0)
14
minh     + pts/2        2026-01-22 21:49 00:07       37993 (14.187.108.34)
15
hoang@fptu-thitkho-cbbz:~$

Users and Groups#

All Linux users are assigned a unique user ID (uid), which is just an integer; normal users start with a uid of 1000 or greater. System users (like root, daemon, bin, etc.) have uids below 1000.

1
hoang@fptu-thitkho-cbbz:~$ id
2
uid=1000(hoang) gid=1000(hoang) groups=1000(hoang),27(sudo)
3
minh@fptu-thitkho-cbbz:~$ id minh
4
uid=1001(minh) gid=1001(minh) groups=1001(minh),27(sudo),100(users)
5
minh@fptu-thitkho-cbbz:~$ id root
6
uid=0(root) gid=0(root) groups=0(root)

• hoang: normal user with uid 1000
• minh: normal user with uid 1001
• root: superuser with uid 0

Linux uses groups for organizing users. Groups are collections of accounts with certain shared permissions; they are used to establish a set of users who have common interests for the purposes of access rights, privileges, and security considerations. Access rights to files (and devices) are granted on the basis of the user and the group they belong to.

One user can belong to multiple groups. Each user has a primary group (usually the same name as the user) and can be a member of additional groups.

1
hoang@fptu-thitkho-cbbz:~$ groups
2
hoang sudo
3
minh@fptu-thitkho-cbbz:~$ groups minh
4
minh sudo users

• hoang belongs to groups: hoang, sudo
• minh belongs to groups: minh, sudo, users

Check all groups in the system:

• /etc/group: Contains all groups, their GIDs, and the users who belong to them as secondary members.
• /etc/passwd: Contains all users, their UIDs, primary GIDs, home directories, and login shells.

1
/etc/passwd
2
hoang:x:1000:1000::/home/hoang:/bin/bash
3

4
/etc/group
5
hoang:x:1000:
6
docker:x:999:hoang
7
sudo:x:27:hoang

User hoang have:

• Primary group: hoang (GID 1000)
• Additional groups: docker, sudo

User → /etc/passwd (UID + primary GID) Group → /etc/group (GID + secondary members)

Adding and Removing Users#

Only the superuser (root) or a user with sudo privileges can add or remove users.

• Adding -> useradd or adduser (more user-friendly)

1
sudo adduser mnhw0612

which, by default, sets the home directory to /home/mnhw0612, populates it with some basic files (copied from /etc/skel) and adds a line to /etc/passwd such as:

mnhw0612:x:1002:1002::/home/mnhw0612:/bin/bash

and sets the default shell to /bin/bash

Check with getent passwd mnhw0612

1
mnhw0612:x:1002:1002:,,,:/home/mnhw0612:/bin/bash

• Removing -> userdel

1
sudo userdel mnhw0612

However, this command does not remove the user’s home directory and mail spool unless the -r option is used, remove user without -r option is useful when you want temporary inactivate an account but preserve the user’s files.

1
sudo userdel -r mnhw0612

Adding and Removing Groups#

Only the superuser (root) or a user with sudo privileges can add or remove groups.

Primary group vs Secondary group:

1
rjsquirrel : rjsquirrel

• User rjsquirrel only have primary group rjsquirrel

1
minh@fptu-thitkho-cbbz:~$ groups minh
2
minh : minh sudo users

• User minh have primary group minh and secondary groups sudo, users

1
# sudo /usr/sbin/groupadd anewgroup
2
sudo groupadd developers

1
sudo usermod -aG groupname username

1
sudo usermod -aG sudo hoang

1
sudo groupdel developers

1
remove-user-from-group

1
rjsquirrel : rjsquirrel anewgroup sudo docker

1
sudo usermod -G sudo,docker rjsquirrel

1
rjsquirrel : rjsquirrel sudo docker

1
sudo gpasswd -d rjsquirrel anewgroup

Order of the Startup Files#

The order in which the startup files are read and executed depends on whether the shell is a login shell or a non-login shell.

1
source ~/.bashrc

nano#

• every linux have nano, if not install yet (very rare), usually in distroless docker image or lightweight linux distros

1
sudo apt-get install nano

1
nano hehe.txt

1
echo "first line" > hihi.txt

1
# Redirection operator
2
echo "first line" >> hihi.txt

1
Ctrl + K

1
Ctrl + 6 #Mark set
2
Alt  + 6  #Copy selected
3
Ctrl + U #Paste

1
Ctrl + K
2
Ctrl + U

vi, vim, nvim#

• More at here (https://viblo.asia/p/co-ban-ve-vim-cho-nguoi-moi-bat-dau-GrLZDavnlk0)
• Vim has 3 mode
  • Normal: default, navigate, simple edit
  • Insert: as the name, using as insert character
  • Command Line: saving, exiting,…

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yy

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3yy

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:%y+

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u

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dd

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3dd

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118796G

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/Error

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gg

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0

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G

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Shift + 0

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:q! #force exit without saving
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:wq #save and exit

The 7 standard Linux file types#

• Regular file

  • -: Normal files such as text, data, or executable files

• Directory

  • d: Files that are lists of others files

• Symbolic Link

  • l : A shortcut that points to the location of the actual file

• Special file

  • c: Mechanism using for input and output, such as file in /dev

• Socket

  • s: A special file that provides inter-process networking protected by the file system’s access control

• Pipe

  • p: A special file that allows processes to communicate with each other without using network socket semantics, FIFO (first in, first out)

• Block Device

  • b: A special file that provides buffered access to hardware devices, such as hard drives

• Example of ls -l output:

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❯ ls -l
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Permissions Size User      Date Modified Name
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drwxrwxr-x     - lcaohoanq 27 Dec  2025   Debian-Hyprland
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lrwxrwxrwx     - lcaohoanq 16 Dec  2025   hoidanit-java-springboot -> /media/data/courses/hoidanit-java-springboot
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drwxr-xr-x     - lcaohoanq 26 Dec  2025   logs_53046524065
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drwxrwxr-x     - lcaohoanq  2 Jan 16:55   meme
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drwxrwxr-x     - lcaohoanq 19 Dec  2025   vagrant-vms
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.rw-r--r--    50 lcaohoanq 14 Dec  2025   .directory
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.rw-rw-r--  1.8k lcaohoanq 24 Dec  2025   .env
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lrwxrwxrwx     - lcaohoanq 16 Dec  2025   '002 #2. Tài liệu khóa học (Project Y).pdf' -> '/media/data/courses/hoidanit-java-springboot/9 - Y - Chapter 1 Bắt buộc xem'/'002 #2. Tài liệu khóa học (Project Y).pdf'
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.rwxrwxr-x   166 lcaohoanq  2 Jan 15:49   4_args.sh
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.rwxrwxr-x   535 lcaohoanq  2 Jan 16:40   6_command_subs.sh
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.rwxrwxr-x   226 lcaohoanq  2 Jan 23:30   18_decision_making.sh
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.rwxrwxr-x   511 lcaohoanq  3 Jan 14:34   21_script_monitoring.sh
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.rw-rw-r--  335k lcaohoanq  2 Jan 21:08   377151058_780890013834619_992292982055176227_n.jpg
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.rwxrwxr-x   390 lcaohoanq  1 Jan 08:36   firstscript.sh
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.rw-rw-r--     5 lcaohoanq 29 Dec  2025   hoang.txt
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.rw-rw-r--  2.1k lcaohoanq  1 Jan 23:46   ig.txt
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.rw-rw-r--  852k lcaohoanq 26 Dec  2025   logs_53046524065.zip
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.rw-rw-r--    81 lcaohoanq 17 Dec  2025   mail.txt
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.rw-rw-r--   151 lcaohoanq 25 Dec  2025   server.txt
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.rw-rw-r--    14 lcaohoanq 25 Dec  2025   test.txt
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.rw-rw-r--  229k lcaohoanq  2 Jan 17:06   ThanhToan_SE181513_LuuCaoHoang_F-Trip2026.jpg
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.rwxr-xr-x  2.1M lcaohoanq 18 Jun  2024   wallhaven-zyggly.jpg
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.rw-rw-r--   885 lcaohoanq  1 Jan 08:49   websetup.sh

• Check the permissions column, first character indicate the file type
  • d: directory
  • l: symbolic link
  • -: regular file
  • .: special file

Grep (Global Regular Expression Print)#

• Find text patterns in files

• Syntax: grep "search_term" [flags] [file_name]

  • grep “mom” hello.txt
  • grep “mom” -n hello.txt (-n: line number)
  • grep “mom” -Rn . (-R: recursive, search multiple file all in current directory)
  • grep “^app” hello.txt (RegEx, search line start with app)
  • grep “error$” mvn_error.log (RegEx, search line end with error)
  • grep -c NullPointerException SomeErrorLogs.txt (count how many time NullPointerException appear in SomeErrorLogs.txt)

• Grep help

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❯ grep --help
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Usage: grep [OPTION]... PATTERNS [FILE]...
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Search for PATTERNS in each FILE.
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Example: grep -i 'hello world' menu.h main.c
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PATTERNS can contain multiple patterns separated by newlines.
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Pattern selection and interpretation:
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  -E, --extended-regexp     PATTERNS are extended regular expressions
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  -F, --fixed-strings       PATTERNS are strings
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  -G, --basic-regexp        PATTERNS are basic regular expressions
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  -P, --perl-regexp         PATTERNS are Perl regular expressions
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  -e, --regexp=PATTERNS     use PATTERNS for matching
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  -f, --file=FILE           take PATTERNS from FILE
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  -i, --ignore-case         ignore case distinctions in patterns and data
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      --no-ignore-case      do not ignore case distinctions (default)
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  -w, --word-regexp         match only whole words
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  -x, --line-regexp         match only whole lines
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  -z, --null-data           a data line ends in 0 byte, not newline
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Miscellaneous:
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  -s, --no-messages         suppress error messages
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  -v, --invert-match        select non-matching lines
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  -V, --version             display version information and exit
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      --help                display this help text and exit
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Output control:
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  -m, --max-count=NUM       stop after NUM selected lines
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  -b, --byte-offset         print the byte offset with output lines
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  -n, --line-number         print line number with output lines
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      --line-buffered       flush output on every line
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  -H, --with-filename       print file name with output lines
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  -h, --no-filename         suppress the file name prefix on output
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      --label=LABEL         use LABEL as the standard input file name prefix
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  -o, --only-matching       show only nonempty parts of lines that match
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  -q, --quiet, --silent     suppress all normal output
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      --binary-files=TYPE   assume that binary files are TYPE;
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                            TYPE is 'binary', 'text', or 'without-match'
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  -a, --text                equivalent to --binary-files=text
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  -I                        equivalent to --binary-files=without-match
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  -d, --directories=ACTION  how to handle directories;
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                            ACTION is 'read', 'recurse', or 'skip'
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  -D, --devices=ACTION      how to handle devices, FIFOs and sockets;
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                            ACTION is 'read' or 'skip'
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  -r, --recursive           like --directories=recurse
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  -R, --dereference-recursive  likewise, but follow all symlinks
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      --include=GLOB        search only files that match GLOB (a file pattern)
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      --exclude=GLOB        skip files that match GLOB
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      --exclude-from=FILE   skip files that match any file pattern from FILE
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      --exclude-dir=GLOB    skip directories that match GLOB
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  -L, --files-without-match  print only names of FILEs with no selected lines
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  -l, --files-with-matches  print only names of FILEs with selected lines
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  -c, --count               print only a count of selected lines per FILE
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  -T, --initial-tab         make tabs line up (if needed)
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  -Z, --null                print 0 byte after FILE name
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Context control:
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  -B, --before-context=NUM  print NUM lines of leading context
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  -A, --after-context=NUM   print NUM lines of trailing context
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  -C, --context=NUM         print NUM lines of output context
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  -NUM                      same as --context=NUM
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      --group-separator=SEP  print SEP on line between matches with context
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      --no-group-separator  do not print separator for matches with context
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      --color[=WHEN],
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      --colour[=WHEN]       use markers to highlight the matching strings;
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                            WHEN is 'always', 'never', or 'auto'
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  -U, --binary              do not strip CR characters at EOL (MSDOS/Windows)
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When FILE is '-', read standard input.  With no FILE, read '.' if
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recursive, '-' otherwise.  With fewer than two FILEs, assume -h.
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Exit status is 0 if any line is selected, 1 otherwise;
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if any error occurs and -q is not given, the exit status is 2.
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Report bugs to: bug-grep@gnu.org
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GNU grep home page: <https://www.gnu.org/software/grep/>
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General help using GNU software: <https://www.gnu.org/gethelp/>

• Usecase 1: We have sample file 0_Run predefined test cases.txt contain the log from Github Action CI pipeline. Search error logs find the error. Problem is the file are too long (10k ~ line), and we are in server, we not have any IDE to use.
• Find text contain “Exception”

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grep "Exception" 0_Run predefined test cases.txt

• Syntax:

  • grep “key_word” -param file_name

• Param

  • R: search recursively
  • n: show line number

• Usecase 2: Find the export port of docker container name pgadmin. We can easily use docker ps then use eyes to look for the pgadmin container. But when the number of container become 50, 100 or even more. Using docker ps and search manually make you look silly :).

• Search with grep + pipe operator |

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❯ docker ps | grep pgadmin
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7ed17a84f912   dpage/pgadmin4   "/entrypoint.sh"         12 days ago   Up 39 minutes             443/tcp, 0.0.0.0:5050->80/tcp, [::]:5050->80/tcp   pgadmin

Sed (non-interactive text editor)#

• Mainly use RegEx, play with RegEx here: https://regex101.com/

• s: subtitution

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❯ sed 's/mom/dad' main.js

• Above command just print the file with replaced part, not a real change

• We use redirection operator to take the output of command then input for sed

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❯ sed 's/mom/dad' main.js > hihi.js

• Using sed at 2nd half pipe, this mean replace all q with vl, g for global search

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❯ echo "lcaohoanqqqq" | sed "s/q/vl/g"
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lcaohoanvlvlvlvl