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README

💻 ++101 Linux commands Open-source eBook

This is an open-source eBook with 101 Linux commands that everyone should know. No matter if you are a DevOps/SysOps engineer, developer, or just a Linux enthusiast, you will most likely have to use the terminal at some point in your career.

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If you need a Linux virtual machine to test these commands on, use the following referral link to get a free $200 Credit For DigitalOcean!

Introduction to Linux eBook

If you are looking for a comprehensive guide for beginners, check out this eBook: Introduction to Linux eBook

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An online copy :zap:🌐 of this ebook is available here 📙.

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Content

Basics

- File Hierarchy Standard (FHS) - Commands

Disk and File System Management

- General Disk Manipulation (non-LVM) - Globs (Wildcards) - Regex - Stream redirection

Text Readers & Editors

- Less - VI

User and Group Management
File System Permissions
SSH
Cronjobs
Package Management

- RPM - YUM

📃 List of commands by category:

- Directory Navigation - File Commands - File and Directory Manipulation - Package archive and compression tools - System commands - Networking Commands - Package Management - User Information commands - Session commands - Getting Help - Applications

📃 List of commands by chapter:
🔗Links
📖Other eBooks
🤲Contributing

Basics

File Hierarchy Standard (FHS)

| Path | Content | | -------- | ----------------------------------- | | /bin | Binaries (User) | | /boot | Static boot loader files | | /etc | Host specific configs | | /lib | Shared libraries and kernel modules | | /sbin | Binaries (System/root) | | /var | Varying files (e.g. Logs) | | /usr | 3rd party software | | /proc | Pseudo file system | | /sys | Pseudo file system | | /mnt | Mountpoint for internal drives | | /media | Mountpoint for external drives | | /home | User homes | | /run | PID files of running processes |

Commands

File System Commands

| Command | Options | Description | | --------------------------------------------------------------------------------------------------------------- | ---------------- | ------------------------------------------------- | | cd | - | Navigate to last dir | | | ~ | Navigate to home | | | ~username | Navigate to home of specified user | | pwd | | Print working dir | | ls | | Print dir content | | | -l | Format as list | | | -a | Show hidden items (-A without . and ..) | | | -r | Invert order | | | -R | Recurse | | | -S | Sort by size | | | -t | Sort by date modified | | mkdir | -p | Create dir with parents | | cp | -r | Copy dir | | rmdir | -p | Remove dir and empty parents | | rm | -rf | Remove dir recursively, -f without confirmation | | mv | | Move recursively | | find | -iname pattern | Search dir/file case-insensitive | | | -mmin n | Last modified n minutes ago | | | -mtime n | Last modified n days ago | | | -regex pattern | Path matches pattern | | | -size n[kMG] | By file size (-n less than; +n greater than) | | | ! searchparams | Invert search |

File Manipulation

| Command | Options | Description | | --------------------------------------------------------------------------------------------------------------- | ------------------------------------------ | ------------------------------------------ | | cat | file | Print content | | tac | file | Print content inverted | | sort | file | Print sorted | | | file -r -u | Print sorted descending without dublicates | | head | -n10 file | Print lines 5-10 | | tail | -f file | Print new lines automatically | | cut | -f -4,7-10,12,15- file | Print selected fields (tab delimited) | | | -c -4,7-10,12,15- file | Print selected characters positions | | | -f 2,4 -d, --output-delimiter=$'\t' file | Change delimiter (but use tab for output) | | uniq | file | Hide consecutive identical lines | | | file -c | Show consecutive identical line count | | | file -u | Hide consecutive identical lines | | file | file | Get file type | | wc | file | Count Lines, Words, Chars (Bytes) |

Archiving

| Command | Options | Description | | --------------------------------------------------------------------------------------------------------------- | -------------------------------- | --------------------------------------------------- | | tar | cfv archiv.tar file1 file2 | Create archive / add or overwrite content | | | tfv archiv.tar | Show content | | | xf archiv.tar [-C ~/extracted] | Extract (and decompress) archive (to ~ / extracted) | | | cfvj archiv.tar.bz2 file | Create bzip2 compressed archive | | | cfvz archiv.tar.gz file | Create gzip compressed archive | | | cfa archiv.tar.[komp] file | create compressed archive (auto type based on name) | | bzip2 | file1 file2 | Dateien (einzeln) komprimieren | | | -d file1 file2 | Compress files (one at a time) | | gzip | file1 file2 | Dateien (einzeln) komprimieren | | | -d file1 file2 | Decompress files |

Disk and File System Management

General Disk Manipulation (non-LVM)

Creating physical partitions is not required! You can create PVs directly!

| Command | Options | Description | | --------------------------------------------------------------------------------------------------------- | ------------------------------------- | ------------------------------------ | | fdisk | -l | List physical disks and partitions | | | /dev/sdb
n | Create new partition | | | /dev/sdb
t
8e | Change partition type to Linux LVM | | mkfs.xfs | /dev/myVG/myVol | Format LV with XFS | | mkfs.ext4 | -f /dev/myVG/myVol | Format LV with EXT4 (overwrite) | | blkid | /dev/myVG/myVol | Show UUID and formatting of volume | | mount | | Show current mounted file systems | | | -t ext4 /dev/myVG/myVol /mountpoint | Mount LV to /mountpoint | | | -a | Mount as configured in /etc/fstab | | umount | | Unmount a file system | | | /dev/myVG/myVol | Unmount LV from /mountpoint | | | /mountpoint | Unmount LV from /mountpoint | | df | - | Show disk usage | | xfs_growfs | /dev/myVG/myVol | Resize xfs filesystem | | resize2fs | /dev/myVG/myVol | Resize ext3/4 filesystem |

Other

| Command | Options | Description | | ----------------------------------------------------------------------------------------------------------- | --------------- | ------------------------------------------ | | <command> | --help | Help of current command (not standardized) | | | -h | | | | -? | | | man | <command> | Manual page of command | | | -k keyword | Search command by keyword (oder apropos) | | alias | | Show aliases | | | name='befehl' | Create alias |

Globs (Wildcards)

The dot . in front of hidden items is ignored by glob patterns!

| Character | Description | | --------- | ----------------------- | | ? | Any single character | | * | Any characters | | [ac-e] | 1 character in enum | | [!ac-e] | 1 character not in enum |

Regex

Bash itself does not know regex. Use programs like grep, sed, awk.

Control characters

| Character | Description | | -------------- | ----------------------- | | . | Any single character | | [ac-e] | 1 character in enum | | [^ac-e] | 1 character not in enum | | ^ | Start of string | | $ | End of string | | \d | Digit | | \D | Not a digit | | \s | Whitespace | | \S | Not a Whitespace | | \< | Start of word | | \> | End of word | | pattern? | Quantifier 0 or 1 | | pattern* | Quantifier 0..n | | pattern+ | Quantifier 1..n | | pattern{x} | Quantifier exactly x | | pattern{x,} | Quantifier x..n | | pattern{x,y} | Quantifier x..y | | pattern{,y} | Quantifier 0..y |

Grep

| Command | Options | Description | | ------------------------------------------------------------------------------------------------------------- | ----------------- | -------------- | | grep | pattern file | Extended Regex | | | -E pattern file | Extended Regex | | | -v pattern file | Invert match | | | -w pattern file | Word match | | | -i pattern file | Ignore case |

Stream redirection

> overwrite
>> append

| Character | Description | | --------------------- | ------------------------------- | | > file or 1> file | STDOUT to file | | < file | Datei to STDIN | | 2> file | STDERR to file | | 2>&1 | STDERR to same target as STDOUT | | > file 2>&1 | STDOUT and STDERR to file |

Text Readers & Editors

Less

| Command | Description | | ------------------- | ------------------------------- | | q | Quit | | R | Refresh content | | F | Auto scroll | | g number | Go to line | | m lowercaseLetter | Mark line | | ' lowercaseLetter | Go to mark | | /pattern | Search forward | | ?pattern | Search backward | | n | Next search result | | N | Last search result | | ESC u | Remove highlighting from search |

VI

VI/VIM Editing

To leave editing mode press ESC.

| Command | Description | | --------- | --------------------- | | i | insert before cursor | | a | insert after cursor | | A | insert at end of line | | o | new line below | | O | new line above | | u | undo | | . | repeat last command | | yy | copy line | | 5yy | copy 5 lines | | p | paste below | | P | paste above | | x | delete character | | 5x | delete 5 characters | | dd | delete line | | 5dd | delete 5 lines | | :10,20d | delete lines 10-20 | | d0 | delete to line begin | | d$ | delete to line end |

Navigation

Navigate as usual with arrow keys, home, end, pg up, pg dn.

| Command | Description | | ------- | ---------------------- | | 5G | go to line 5 | | H | go to top of screen | | M | go to middle of screen | | L | go to end of screen | | 5w | move over 7 words | | 5b | move back 5 words |

Other

| Command | Description | | ----------- | ---------------------------- | | /foo | search forward | | ?foo | search backwards | | n | repeat search | | :w | save | | :q | close | | :wq | save and close | | :q! | close without saving | | :!command | run bash command | | :r foo | read file foo into this file |

User and Group Management

UID

| UID | Type | | ----- | -------------- | | <1000 | system account | | >1000 | user account |

User Database

User info without passwords is stored in /etc/passwd.

| username | PW | UID | GID | GECOS | HOME | SHELL | | -------- | --- | ---- | ---- | ----- | ----------- | --------- | | hfict | x | 1000 | 1000 | | /home/hfict | /bin/bash |

Group Database

Group info with secondary group members are stored in /etc/group. Primary group members are identified by GID in user database.

| groupname | PW | GID | Users | | --------- | --- | --- | ----------- | | wheel | x | 10 | hfict,user2 |

Password Database

Hashed user passwords are stored in /etc/shadow. Password encryption is configured in /etc/login.defs.

| username | PW | Last PW change | Minimum | Maximum | Warn | Inactive | Expire | | -------- | ------ | -------------- | ------- | ------- | ---- | -------- | ------ | | hfict | [hash] | 17803 | 0 | 99999 | 7 | | |

PW:

[hash] Encrypted test password
! [hash] Account locked
!! or * Account locked, no password set

Commands

| Command | Param | Description | | ------------------------------------------------------------------------------------------------------------------- | --------------------------------------------- | ----------------------------------------------------- | | id | username | Show a user's ID and groups | | who | | Show logged in users | | last | | Show last logins | | lastb | | Show last failed logins | | sudo | -u user command | Execute command with user rights (default is root) | | | -i or su - | Shell with root rights | | su | | Shell as root (non-login shell) | | | - | Shell as root (login shell) | | | - user | Shell as user | | useradd | -u 2101 -g primarygroup -c comment username | Create user (without -g, new group will be created) | | usermod | -G group1, group2 | Define (overwrite) secondary groups | | | -ag group, group2 | Add secondary groups | | | -l username | Change username | | | -L | Lock Account | | | -U | Unlock Account | | | -s shellpath | Change shell | | userdel | -r username | Delete user including home and mail spool | | passwd | username | Change password (interactive) | | groupadd | groupname | Create group (optionally set GID with -g) | | groupdel | groupname | Delete group |

File System Permissions

Permissions can be set on:

User (owner)
Group (owner)
Others

Only root can change User. User can change Group.

Basic permissions (Add binary flags to combine):

| Char | Binary Flag | Permission | | ---- | ----------- | ---------- | | r | 4 | read | | w | 2 | write | | x | 1 | execute |

Advanced permissions (place in front of basic permissions: chmod 1777 shared).:

| Char | Binary Flag | Name | Description | | ----- | ----------- | ---------- | -------------------------------------------------------------------------- | | t / T | 1 | Sticky Bit | Others can't delete content (only applicable for directories) | | s / S | 2 | SGID-Bit | File: run with permissions of Group
Dir: New elements inherit Group | | s / S | 4 | SUID-Bit | File is run with permissions of User (only applicable for files) |

Advanced permissions replace the x when using ls -l. Lower case if x is set, upper case if x is not set.

Read permission on a directory only allows to see the directory itself but not it's contents. Use execute permission to show contents.

Commands

| Command | Options | Description | | --------------------------------------------------------------------------------------------------------------- | ------------------------ | ------------------------------------------------- | | chmod | -R [uog] dirname | Set permissions recursively using binary flags | | | +[suog] filename | Add permissions using binary flags | | | -[suog] filename | Remove permissions using binary flags | | | u+x filename | Add execute permission for User | | | g+wx filename | Add write and execute permissions for Group | | | o-r filename | Remove read permission for Others | | chown | -R user:group filename | Change owner (User & Group_) recursively | | | user filename | Change owner (User) | | | :group filename | Change owner (Group) | | chgroup | group filename | Change owner (Group) |

SSH

SSH Configuration is done in /etc/ssh/sshd_config.

Reload SSH service with systemctl reload sshd to apply changes!

DenyUsers, AllowUsers, DenyGroups, AllowGroups override each other and are applied in the order listed above.

| Config | Option | Description | | ----------------- | ------------------ | --------------------------------------------- | | PermitRootLogin | no | Deny root to login via SSH | | | yes | Allow root to login via SSH | | | without-password | Allow only with private/public key auth | | AllowUsers | user1 user2 | Allow only user1 and user2 | | DenyUsers | user1 user2 | Allow all users but user1 and user2 | | AllowGroups | group1 group2 | Allow only users from specified groups | | DenyGroups | group1 group2 | Allow all users but those in specified groups |

Cronjobs

Crontab

Cronjobs are configured in crontab files. Do not edit these files directly. Use crontab -e instead. This runs all required actions to activate a cronjob after saving the edited crontab. The locations are as follows:

/var/spool/cron/username user specific
/etc/crontab system wide crontab

The format of the files is (user specific crontabs do not have the column user-name):

Example of job definition:
.---------------- minute (0 - 59 | */5 [every 5 minutes])
|  .------------- hour (0 - 23)
|  |  .---------- day of month (1 - 31)
|  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
|  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
|  |  |  |  |
        * user-name  command to be executed

| Command | Description | | -------------------------------- | ----------------------------- | | rpm -q cronie | Check if package is installed | | systemctl status crond.service | Check if service is running | | crontab -l | List current users crontab | | crontab -e | Edit current users crontab | | crontab -e -u username | Edit specific users crontab | | crontab -r | Remove current users crontab |

Script folders

Scripts in one of the following directories will be executed at the interval specified by the directory's name:

/etc/cron.hourly
/etc/cron.daily
/etc/cron.weekly
/etc/cron.monthly

Allow / Deny usage

Add user names one per line to the following files:

/etc/cron.allow Whitelist
/etc/cron.deny Blacklist

If none of the files exists, all users are allowed.

Logs and Results

Execution of cronjobs is logged in /var/log/cron. Results are sent to the users mail /var/spool/mail/username.

Package Management

RPM

RPM

| Command | Description | | ------------------------ | ----------------------------------------- | | rpm -i rpmfile\|rpmurl | Install package | | rpm -e packagename | Uninstall package | | rpm -q packagename | Check if package is installed | | rpm -ql packagename | List files in a package | | rpm -qa | List all installed packages | | rpm -qf /path/to/file | Get package that installed the file | | rpm -qf $(which <exe>) | Get package that installed the executable | | rpm -V packagename | Validate installed package |

YUM

YUM is configured in /etc/yum.conf

Repos are configured in /etc/yum.repos.d/

Log is in /var/log/yum.log

| Command | Description | | ------------------------------------- | ----------------------------------------- | | yum install packagename [-y] | Install package (-y no confirm message) | | yum remove packagename | Uninstall package | | yum update | Update all installed packages | | yum update packagename | Update specific package | | yum update pattern* | Update packages using wildcard | | yum info packagename | Get detailed info about package | | yum list packagename | List installed and available packages | | yum search searchstring | search for a package (name & summary) | | yum search all searchstring | search for a package (all infos) | | yum deplist packagename | List dependencies of a package | | yum reinstall packagename | Reinstall (corrupted) package | | yumdownloader --resolve packagename | Download rpm package with dependencies |