Some Useful and less know #Linux commands

1. cal: Display a #calendar for the current or specified month.

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   cal

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2. units: Convert units from one measurement to another.

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

   units "feet to meters"

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3. figlet: Create text banners using ASCII art fonts.

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   figlet Hello, Linux!

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4. toilet: Generate text-based art and banners.

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   toilet -f term Hello, Linux!

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5. cowsay: Display text in speech bubbles from an ASCII art cow.

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

   cowsay "Moo, I'm a cow!"

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6. sl: Display a steam locomotive in the terminal when you mistype `ls`.

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

   sl

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7. rev: Reverse the order of characters in a file or string.

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

   echo "Linux" | rev

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8. fortune: Get a random, often humorous, text message.

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

   fortune

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9. yes: Output a continuous stream of "yes" until manually stopped.

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

   yes

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

   

10. watch: Execute a command repeatedly and display the output in real-time.

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

    watch -n 1 "date"

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11. cmatrix: Display the falling characters similar to "The Matrix."

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

    cmatrix

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12. slurm: Network bandwidth usage monitoring.

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

    slurm -i eth0

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13. qrencode: Generate QR codes from text.

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

    qrencode -o qr.png "https://www.example.com"

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14. lshw: List hardware information.

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

    lshw

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15. tree: Display directory structure in a tree-like format.

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

    tree /path/to/directory

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16. apropos: Search man page names and descriptions for keywords.

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

    apropos keyword

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17. ranger: A console-based file manager with VI keybindings.

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

    ranger

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18. htop: An interactive process viewer and system monitor.

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

    htop

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

19. ncdu: A disk usage analyzer with an ncurses interface.

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

    ncdu

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20. tldr: A simplified and community-driven man pages.

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

    tldr command

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These less-known Linux commands and utilities can be fun to explore and might help you perform various tasks more efficiently or just bring a smile to your face with some terminal-based humor.

#LinuxCommands,#HiddenCommands,#TerminalTricks,#LinuxUtilities,#UsefulCommands,#CommandLineFun,#LinuxTips,#ASCIIArt,#TextBanners,#LinuxTools

List of commonly used #Docker #CLI (#Command-Line Interface) #commands

Troubleshooting process-related issues in Linux often involves various commands and checks. Here are some important Linux commands for process troubleshooting

1. **List Running Processes:** Use `ps aux` or `top` to list currently running processes.

2. **Check Process Details:** Use `ps -p <PID>` to view detailed information about a specific process.

3. **Kill a Process:** Use `kill` or `killall` to terminate processes, e.g., `kill <PID>`.

4. **Find Process by Name:** Use `pgrep` to find processes by name, e.g., `pgrep <process_name>`.

5. **View Process Tree:** Use `pstree` to display the process tree.

6. **Check Process Limits:** Use `ulimit -a` to view process-level resource limits.

7. **Check Process CPU Usage:** Use `htop` or `top` to monitor CPU usage by processes.

8. **Check Process Memory Usage:** Use `htop` or `top` to monitor memory usage by processes.

9. **Check Process Disk I/O:** Use `iotop` to monitor disk I/O by processes.

10. **Check Process Network Activity:** Use `iftop` or `nethogs` to monitor network activity by processes.

11. **Check Process Priority:** Use `nice` and `renice` to set or adjust process priority.

12. **Check Open Files by Process:** Use `lsof` to list open files and sockets by process.

13. **Check Process Environment:** Use `cat /proc/<PID>/environ` to view the environment variables of a process.

14. **Check Process Threads:** Use `ps -p <PID> -L` to list threads of a process.

15. **Check Process Dependencies:** Use `ldd` to list shared library dependencies of a binary.

16. **Monitor Process Resource Usage:** Use `sar` or `pidstat` to monitor various resource usage by processes.

17. **Check Process Start Time:** Use `ps -p <PID> -o lstart` to check the start time of a process.

18. **Check Zombie Processes:** Use `ps aux | grep 'Z'` to identify and handle zombie processes.

19. **Check Process Traces:** Use `strace` or `ltrace` to trace system or library calls made by a process.

20. **Process Management with systemd:** Use `systemctl` to start, stop, enable, or disable services and processes managed by systemd.

#ProcessIssues, #ProcessTroubleshooting, #ProcessManagement, #ProcessMonitoring, #ResourceUsage, #ProcessTree, #KillProcess, #CPUUsage, #MemoryUsage, #DiskIO, #NetworkActivity, #ProcessPriority, #OpenFiles, #EnvironmentVariables, #ProcessThreads, #DependencyAnalysis, #ResourceMonitoring, #ZombieProcesses, #ProcessTracing, #SystemdServices

Some tips and tricks for using the `#sudo` #command

1. Limit Access: By default, `sudo` allows authorized users to execute any command with elevated privileges. You can restrict access to specific commands or command categories by editing the `/etc/sudoers` file using the `visudo` command. For example, to allow a user to only run the `reboot` command:

 

   username ALL=/sbin/reboot

 

2. Customize the Prompt: You can customize the `sudo` command prompt to display a warning message or provide context for the command being executed. Edit the `sudoers` file and add a `Defaults` line with the `lecture` option:

 

   Defaults        lecture=always

   Defaults        lecture_file=/etc/sudo_lecture

 

3. Timestamp and Timeout: By default, `sudo` caches your credentials for a certain period (usually 5 minutes) to avoid repetitive password prompts. You can adjust the timeout duration by editing the `sudoers` file:

 

   Defaults        timestamp_timeout=10

 

4. Check User Privileges: You can verify which commands a user can run with `sudo` privileges by running:

 

   sudo -l

 

5. Running GUI Applications: If you need to run graphical applications with `sudo`, use `sudo -H` or `sudo -i` to set the `HOME` environment variable correctly:

 

   sudo -H gedit

 

6. Avoid `sudo su`: Instead of running `sudo su` to become the root user interactively, use `sudo -i` or `sudo -s` for a shell session with elevated privileges. This avoids potential issues with environment variables.

 

   sudo -i

 

7. Audit `sudo` Usage: You can enable auditing of `sudo` commands to keep track of who is using `sudo` and what commands are executed. Refer to your system's auditd or auditctl configuration for this.

8. Use `sudo !!`: If you forget to prefix a command with `sudo`, you can run it with elevated privileges using `sudo !!`. For example:

 

   apt update

   sudo !!  # Executes 'sudo apt update'

 

9. Secure Password Entry: To ensure your password is hidden while entering it for `sudo`, use the `-S` option:

 

   sudo -S command

 

10. Temporary Elevation: If you need to run multiple commands as the superuser in the same terminal session, you can use `sudo -s` to start an elevated shell:

  

    sudo -s

  

11. Insider Information: To display information about the user's `sudo` privileges, run:

  

    sudo -l

  

12. Enable Root Account: You can enable and set a password for the root account, but this is generally discouraged in favor of using `sudo`.

Remember that with great power comes great responsibility. Always use `sudo` cautiously to avoid unintentional system changes or security risks.

#Linux #Commands by #Category : #AllLinuxCommand #linux...Linux

#FileOperation

#ls : List files in a directory.

#cp: Copy a file.

#mv: Rename (“move”) a file.

#rm: Delete (“remove”) a file.

#ln: Create links (alternative names) to a file.

#shred: Completely erase a file when the file is deleted

#DirectoryOperation

#cd: Change your current directory.

#pwd: Print the name of your current directory.

#basename: Print the final part of a file path.

#dirname: Print a file path without its final part.

#mkdir: Create (make) a directory.

#rmdir: Delete (remove) an empty directory.

#rm -r: Delete a nonempty directory and its contents.

#ViewingFiles

#cat: View files in their entirety. cat [filename]

#less: View text files one page at a time. less [filename]

#head: View the first lines of a text file. head [filename]

#tail:  View the last lines of a text file. tail [filename]

#nl: View text files with their lines numbered. nl [filename]

#strings: Display text that’s embedded in a binary file. strings [filename]

#od: View data in octal (or other formats). oc [filename]

#xxd: View data in hexadecimal.xxx [filename]

#gv: View PostScript or PDF files. sudo apt install gv [filename]

#xdvi: View TeX DVI files. sudo apt install xdiv xdiv [filename]

#JobControl #commands

#jobs: List your jobs.

#&: Run a job in the background.

#^Z: Suspend the current (foreground) job.

#suspend: Suspend a shell.

#fg: Un-suspend a job: bring it into the foreground.

#bg: Make a suspended job run in the background.

#kill -STOP/-CONT : pausing continuing process

#FileCreation and #Editing

#Vim: Open file/ Create a File

#Vi : Open File/ Create a File.

#Nano : Open File/ Create a File

#Emacs : Open/Create File

#Edit: Graphical File Editor

#Ed: is a line-oriented text editor. It is used to create, display, modify and text files

#File Property Commands

#stat: Display attributes of files and directories.

#wc: Count bytes, words, lines in a file.

#du: Measure disk usage of files and directories.

#file: Identify (guess) the type of a file.

#touch: Change timestamps of files and directories.

#chown: Change owner of files and directories.

#chgrp: Change group ownership of files and directories.

#chmod: Change protection mode of files and directories.

#umask: Set a default mode for new files and directories.

#chattr: Change extended attributes of files and directories.

#lsattr: List extended attributes of files and directories.

#SearchingFiles #Location

#find: Locate files in a directory hierarchy.

#xargs: Process a list of located files (and much more).

#locate: Create an index of files, and search the index for string.

#which: Locate executables in your search path (command).

#type: Locate executables in your search path (bash built-in).

#whereis: Locate executables, documentation, and source files.

#File content manipulation 

#grep: Find lines in a file that match a regular expression.

#cut: Extract columns from a file.

#paste: Append columns.

#tr: Translate characters into other characters.

#sort: Sort lines of text by various criteria.

#uniq: Locate identical lines in a file.

#tee: Copy a file and print it on standard output, simultaneously.

#File #Compression and #Packaging

#tar: Package multiple files into a single file.

#gzip: Compress files with GNU Zip.

#gunzip: Uncompress GNU Zip files.

#bzip2: Compress files in BZip format.

#bunzip2: Uncompress BZip files.

#bzcat: Compress/uncompress BZip files via standard input/output.

#compress: Compress files with traditional Unix compression.

#uncompress: Uncompress files with traditional Unix compression.

#zcat: Compress/uncompress file via standard input/output (gzip or compress).

#zip: Compress files in Windows Zip format.

#unzip: Uncompress Windows Zip files.

#metamail: Extract MIME data to files.

#Filescomparision

#diff: Line-by-line comparison of two files or directories.

#comm: Line-by-line comparison of two sorted files.

#cmp: Byte-by-byte comparison of two files.

#md5sum: Compute a checksum of the given files (MD5).

#Printer/#Printing 

#lpr: Print a file.

#lpq: View the print queue.

#lprm: Remove a print job from the queue.

#Spelling Checking

#look: Look up the spelling of a word quickly.

#aspell: Interactive spelling checker.

#spell: Batch spelling checker.

#Disk and #FileSystem

#df: Show information about the file system on which each FILE resides, or all file systems by default.

#du : Summarize disk usage of the set of FILEs, recursively for directories.

#mount: Make a disk partition accessible.

#umount: Unmount a disk partition (make it inaccessible).

#fsck: Check a disk partition for errors.

#sync: Flush all disk caches to disk.

#lshw :List all hardware

#lsblk :List information about block devices. 

#findmnt: Find a (mounted) filesystem.

#blkid : locate/print block device attributes

#fdisk : Display or manipulate a disk partition table.

#mkfs: Make file filesystem

#mkswap: Make a swap area on a device or in a file

#parted: Disk partitioning and partition resizing program.  It allows the user to create, destroy, resize, move and copy ext2, ext3, Linux-swap,  FAT  and FAT32 partitions.

#sfdisk: List the size of a partition, the partitions on a device, check the partitions on a device, and repartition a device.

#file: Determine type of FILEs

#Backup and #Remote #Storage

#dump: Write a disk partition to a backup medium.

#restore: used for restoring files from a backup created using dump.

#cdrecord: record audio or data CD, DVD or BluRay

#rsync: is a file transfer program capable of efficient remote update via a fast differencing algorithm.

#mt: Control magnetic tape drive operation.

#cpio: copies files to and from archives

#cp/scp : copy/ remote copy files

#dd: in simplest terms copies an image of a selected disk area. Then provides the ability to copy selected blocks of a physical disk.

#tar/zip/gzip : compress files

#Monitoring #Linux system

#ps: List process.

#uptime: View the system load.

#w: List active processes for all users.

#top: Monitor resource-intensive processes interactively.

#htop: utility that allows the user to interactively monitor the system's vital resources or server's processes in real time.

#iotop: display and monitor the disk IO usage details and even gets a table of existing IO utilization by the process

#gnome-system-monitor: Monitor system load and processes graphically.

#xload: Simple, graphical monitor of system load.

#free: Display free memory.

#pidof: Command, which looks up and prints the PID of a process by its name

#nmon: fully interactive performance monitoring command-line utility tool for Linux. It is a benchmark tool that displays performance about the CPU, MEMORY, NETWORK, DISKS, FILE SYSTEM, NFS, TOP PROCESSES, RESOURCES, AND POWER MICRO-PARTITION

#lsof : display a list of all the open files and the processes. The open files included are disk files, network sockets, pipes, devices, and processes.

#iostat: Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.

#Psacct or Acct : monitor user activities

#whowatch – Monitor Linux Users and Processes in Real Time

#vmstat: display statistics of virtual memory, kernel threads, disks, system processes, I/O blocks, interrupts, CPU activity, and much more

#Network Related

#traceroute: View the network path to a remote host.

#ifconfig: Older command to set and display network interface information.

#netstat: list of all active connections.

#who: List logged-in users, long output.

#tcpdump: listing of all active connections.

#ping: Check if a remote host is reachable.

#ifup/ifdown/ifquery: actives/deactivates/query about state of a network interface.

#nslookup: queries Internet name servers interactively for information.

#dig: stands for Domain Information Groper. It is used for retrieving information about DNS name servers.

#mtr: combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

#ip: used for displaying and manipulating routing, network devices, interfaces.

#ethtool: utility for querying and modifying network interface controller parameters and device drivers.

#route: utility for displaying or manipulating the IP routing table of a Linux system.

#nmcli: scriptable command-line tool to report network status, manage network connections, and control the NetworkManager.

#ss: utility to investigate sockets. It dumps socket statistics and displays information similar to netstat.

#nc: also referred to as the “Network Swiss Army knife”, is a powerful utility used for almost any task related to TCP, UDP, or UNIX-domain sockets. It is used to open TCP connections, listen on arbitrary TCP and UDP ports, perform port scanning plus more.

#host: command is a simple utility for carrying out DNS lookups, it translates hostnames to IP addresses and vice versa.

#Instant #Messaging

#write: Send messages to a terminal.

#mesg: Prohibit talk and write.

#tty: Print your terminal device name.

#wall:  allow us to send messages to another user in the terminal using tty2

#Web #Browsing

#lynx: open source command line browser 

#Links2: text-based browser that you can easily utilize on your terminal with a good user experience.

#elinks: eLinks is similar to Links2 — but it is no longer maintained.

#wget: non-interactive network downloader which is used to download files from the server 

#curl: (short for "Client URL") is a command line tool that enables data transfer over various network protocols

#W3M: open-source text-based web browser for the terminal.

#Email:

#mail: mail command is quite popular and is commonly used to send emails from the command line.

#mailx: Mailx is the newer version of mail command and was formerly referred to as nail in other implementations.

#mutt: Mutt is a lightweight Linux command line email client. Unlike the mail command that can do basic stuff, mutt can send file attachments.

#mpack: mpack command is used to encode the file into MIME messages and sends them to one or several recipients, or it can even be used to post to different newsgroups.

#sendmail: a most popular SMTP server used in most of Linux/Unix distribution. Sendmail allows sending email from command line.

#swaks: command is a scriptable, flexible, transaction-oriented SMTP tool. 

#ssmtp:  send emails using the SMTP server from the Linux terminal.

#Network Connection

#ssh: Securely log into a remote host, or run commands on it.

#telnet: Log into a remote host (insecure!).

#scp: Securely copy files to/from a remote host (batch).

#sftp: Securely copy files to/from a remote host (interactive).

#ftp: Copy files to/from a remote host (interactive, insecure!).

#Host Location

#host: Look up hostnames, IP addresses, and DNS info.

#whois: Look up the registrants of Internet domains.

#ping: Check if a remote host is reachable.

#traceroute: View the network path to a remote host.

#dig: dig is a tool for querying DNS nameservers 

#Host Information:

#uname: Print basic system information.

#lshw: extract detailed information on the hardware configuration of the machine

#lscpu: gathers CPU architecture information from sysfs, /proc/cpuinfo and any applicable architecture-specific libraries

#lsblk: lists information about all available or the specified block devices

#lsusb: displaying information about USB buses in the system and the devices connected to them

#lspci: utility for displaying information about PCI buses in the system and devices connected to them

#dmidecode: hardware information by reading data from the DMI tables

#hostname: Print the system’s hostname.

#dnsdomainname: Same as hostname -d.

#domainname: Same as hostname -y.

#nisdomainname: Same as hostname -y.

#ypdomainname: Same as hostname -y.

#ip: Set and display network interface information.

#ifconfig: Older command to set and display network interface information.

#hwinfo is used to probe for the hardware present in the system. It can be used to generate a system overview log which can be later used for support.

#User Management 

#useradd: Create an account.

#userdel: Delete an account.

#usermod: Modify an account.

#passwd: Change a password.

#chfn: Change a user’s personal information.

#chsh: Change a user’s shell.

#Group Management

#groups: Print the group membership of a user.

#groupadd: Create a group.

#groupdel: Delete a group.

#groupmod: Modify a group.

#User and Environment:

#logname: Print your login name.

#whoami:  Print your current, effective username.

#id: Print the user ID and group membership of a user.

#who: List logged-in users, long output.

#users: List logged-in users, short output.

#finger: Print information about users.

#last: Determine when someone last logged in.

#printenv: Print your environment.

#Login Logout Shutdown Reboot 

#shutdown: arranges for the system to be brought down in a safe way,All logged-in users are notified that the system is going down and, within the last five minutes of TIME, new logins are prevented.

#reboot: This will reboot the system immediately

#pm-hibernate/systemctl hibernate: Most of the computer’s hardware is not capable of Hibernation. You can enter the pm-hibernate command and check.

#init 0 : Shutsdown the system

#init 6 : will reboot the system

#systemctl [halt/poweroff/reboot/suspend/hibernate] : uses systemctl command to perform action

#halt/halt -p: command allows you to halt the system, without actually powering down. if we use -p it will power off too

#poweroff: command which allows you to power off the system after shutting down.

#Scheduling jobs in Linux

#sleep: Wait a set number of seconds, doing nothing.

#watch: Run a program at set intervals.

#at: Schedule a job for a single, future time.

#crontab: Schedule jobs for many future times.

#Controlling Process:

#kill: Terminate a process (or send it a signal).

#killall: When started by a root user, the killall command cancels all cancellable processes except those processes that started it

#nice:  Invoke a program at a particular priority.

#renice: Change a process’s priority as it runs.

#cpulimit: interrupt execution of a process (or process group) if the CPU/system load goes beyond a defined threshold.

#ulimit: Used to define various limits on files/process/memory etc