% http://linoxide.com/guide/linux-command-shelf.html

1. SYSTEM

  $ uname –a                       => Display linux system information
  $ uname –r                       => Display kernel release information (refer uname command in detail)
  $ cat /etc/redhat_release        => Show which version of redhat installed 
  $ uptime                         => Show how long system running + load (learn uptime command)
  $ hostname                       => Show system host name
  $ hostname -i                    => Display the IP address of the host (all options hostname)
  $ last reboot                    => Show system reboot history (more examples last command)
  $ date                           => Show the current date and time (options of date command)
  $ cal                            => Show this month calendar (what more in cal)
  $ w                              => Display who is online (learn more about w command)
  $ whoami                         => Who you are logged in as (example + sreenshots)
  $ finger user                    => Display information about user (many options of finger command)

2. HARDWARE

  $ dmesg                          => Detected hardware and boot messages (dmesg many more options)
  $ cat /proc/cpuinfo              => CPU model
  $ cat /proc/meminfo              => Hardware memory
  $ cat /proc/interrupts           => Lists the number of interrupts per CPU per I/O device
  $ lshw                           => Displays information on hardware configuration of the system
  $ lsblk                          => Displays block device related information in Linux (sudo yum install util-linux-ng)
  $ free -m                        => Used and free memory (-m for MB) (free command in detail)
  $ lspci -tv                      => Show PCI devices (very useful to find vendor ids)
  $ lsusb -tv                      => Show USB devices (read more lsusb options)
  $ lshal                          => Show a list of all devices with their properties 
  $ dmidecode                      => Show hardware info from the BIOS (vendor details)
  $ hdparm -i /dev/sda              # Show info about disk sda 
  $ hdparm -tT /dev/sda            # Do a read speed test on disk sda
  $ badblocks -s /dev/sda          # Test for unreadable blocks on disk sda

3. STATISTICS

  $ top                              => Display and update the top cpu processes (30 example options)
  $ mpstat 1                         => Display processors related statistics (learn mpstat command)
  $ vmstat 2                         => Display virtual memory statistics (very useful performance tool)
  $ iostat 2                         => Display I/O statistics (2sec Intervals) (more examples)
  $ tail -n 500 /var/log/messages    => Last 10 kernel/syslog messages (everyday use tail options)
  $ tcpdump -i eth1                  => Capture all packets flows on interface eth1 (useful to sort network issue)
  $ tcpdump -i eth0 'port 80'        => Monitor all traffic on port 80 ( HTTP )
  $ lsof                             => List all open files belonging to all active processes.(sysadmin favorite command)
  $ lsof -u testuser                 => List files opened by specific user
  $ free –m                          => Show amount of RAM (daily usage command)
  $ watch df –h                      => Watch changeable data continuously(interesting linux command)

4. USERS

  $ id                                  => Show the active user id with login and group(with screenshot)
  $ last                                => Show last logins on the system (few more examples)
  $ who                                 => Show who is logged on the system(real user who logged in)
  $ groupadd   admin                    => Add group "admin" (force add existing group)
  $ useradd -c  "Sam Tomshi" -g admin -m sam  => Create user "sam" and add to group "admin"(here read all parameter)
  $ userdel sam                         => Delete user sam (force,file removal)
  $ adduser sam                         => Add user "sam" 
  $ usermod                             => Modify user information(mostly useful for linux system admins)

5. FILE COMMANDS

  $ ls –al                                => Display all information about files/ directories(20 examples)
  $ pwd                                   => Show current directory path(simple but need every day)
  $ mkdir directory-name                  => Create a directory(create mutiple directory)
  $ rm file-name                          => Delete file(be careful of using rm command)
  $ rm -r directory-name                  => Delete directory recursively 
  $ rm -f file-name                       => Forcefully  remove file
  $ rm -rf directory-name                 => Forcefully remove directory recursively
  $ cp file1 file2                        => Copy file1 to file2 (15 cd command examples)
  $ cp -r dir1 dir2                       => Copy dir1 to dir2, create dir2 if it doesn’t  exist
  $ mv file1 file2                        => Move files from one place to another(with 10 examples)
  $ ln –s  /path/to/file-name  link-name  => Create symbolic link to file-name (examples)
  $ touch file                            => Create or update file (timestamp change)
  $ cat > file                            => Place standard input into file (15 cat command examples)
  $ more file                             => Output the contents of file (help display long tail files)
  $ head file                             => Output the first 10 lines of file (with different parameters)
  $ tail file                             => Output the last 10 lines of file (detailed article with tail options)
  $ tail -f file                          => Output the contents of file as it grows starting with the last 10 lines
  $ gpg -c file                           => Encrypt file (how to use gpg)
  $ gpg file.gpg                          => Decrypt file

6. PROCESS RELATED

  $ ps                               # Display your currently active processes (many parameters to learn)
  $ ps aux | grep 'telnet'           # Find all process id related to telnet process
  $ pmap                             # Memory map of process (kernel,user memory etc)
  $ top                              # Display all running processes (30 examples)
  $ kill pid                         # Kill process with mentioned pid id (types of signals)
  $ killall proc                     # Kill all processes named proc
  $ pkill processname                # Send signal to a process with its name
  $ bg                               # Resumes suspended jobs without bringing them to foreground (bg and fg command)
  $ fg                               # Brings the most recent job to foreground
  $ fg n                             # Brings job n to the foreground

7. FILE PERMISSION RELATED

  $ chmod octal file-name     # Change the permissions of file to octal , which can be found separately for user, group and world
  octal value  (more examples)
  4 - read
  2 – write
  1 – execute
  Example 
  $ chmod 777 /data/test.c                   # Set rwx permission for owner , rwx  permission for group, rwx permission for world
  $ chmod 755 /data/test.c                   # Set rwx permission for owner,rx for group and world
  $ chown owner-user file                    # Change owner of the file (chown more examples)
  $ chown owner-user:owner-group  file-name  # Change owner and group owner of the file
  $ chown owner-user:owner-group directory   # Change owner and group owner of the directory
  Example 
  $ chown bobbin:linoxide test.txt
  $ ls -l test.txt
  -rw-r--r-- 1 bobbin linoxide 0 Mar 04 08:56 test.txt

8. NETWORK

  $ ifconfig –a                  # Display all network ports and ip address (set mtu and other all options)
  $ ifconfig eth0                # Display specific  ethernet port ip address and details
  $ ip addr show                 # Display all network interfaces and ip address(available in iproute2 package,powerful than ifconfig)
  $ ip address add 192.168.0.1 dev eth0      # Set ip address
  $ ethtool eth0                 # Linux tool to show ethernet status (set full duplex , pause parameter)
  $ mii-tool  eth0               # Linux tool to show  ethernet status (more or like ethtool)
  $ ping host                    # Send echo request to test connection (learn sing enhanced ping tool)
  $ whois domain                 # Get who is information for domain
  $ dig domain                   # Get DNS information for domain (screenshots with other available parameters)
  $ dig  -x host                 # Reverse lookup host 
  $ host google.com              # Lookup DNS ip address for the name (8 examples of host command)
  $ hostname –i                  # Lookup local ip address (set hostname too)
  $ wget file                    # Download file (very useful other option)
  $ netstat  -tupl               # Listing all active listening ports(tcp,udp,pid) (13 examples)

9. COMPRESSION / ARCHIVES

  $ tar cf home.tar  home              # Create tar named home.tar containing home/ (11 tar examples)
  $ tar xf file.tar                    # Extract the files from file.tar
  $ tar czf  file.tar.gz  files        # Create a tar with gzip compression
  $ gzip file                          # Compress file and renames it to file.gz (untar gzip file)

10. INSTALL PACKAGE

  $ rpm -i pkgname.rpm                         # Install rpm based package (Installing, Uninstalling, Updating, Querying ,Verifying)
  $ rpm -e pkgname                             # Remove package
  Install from source
  ./configure
  make
  make install (what it is)

11. SEARCH

  $ grep pattern files                 # Search for pattern in files (you will this command often)
  $ grep  -r pattern dir                # Search recursively for pattern in dir
  $ locate file                        # Find all instances of file
  $ find /home/tom -name 'index*'      # Find files names that start with "index"(10 find examples)
  $ find /home -size +10000k           # Find files larger than 10000k in /home

12. LOGIN (SSH AND TELNET)

  $ ssh user@host                         # Connect to host as user (secure data communication command)
  $ ssh  -p port user@host                # Connect to host using specific port
  $ telnet host                           # Connect to the system using  telnet port

13. FILE TRANSFER

  scp
  $ scp file.txt   server2:/tmp                   # Secure copy file.txt to remote host  /tmp folder
  $ scp nixsavy@server2:/www/*.html   /www/tmp    # Copy *.html files from remote host to current system /www/tmp folder
  $ scp -r nixsavy@server2:/www   /www/tmp        # Copy all files and folders recursively from remote server to the current system /www/tmp folder
  rsync
  $ rsync -a /home/apps /backup/                  # Synchronize source to destination
  $ rsync -avz /home/apps linoxide@192.168.10.1:/backup    # Synchronize files/directories between the local and remote system with compression enabled

14. DISK USAGE

  $ df –h                         # Show free space on mounted filesystems(commonly used command)
  $ df -i                         # Show free inodes on mounted filesystems
  $ fdisk -l                  # Show disks partitions sizes and types(fdisk command output)
  $ du -ah                        # Display disk usage in human readable form (command variations)
  $ du -sh                        # Display total disk usage on the current directory
  $ findmnt                        # Displays target mount point for all filesystem (refer type,list,evaluate output)
  $ mount device-path mount-point  # Mount a device 

15. DIRECTORY TRAVERSE

  $ cd ..                              # To go up one level of the directory tree(simple & most needed)
  $ cd                                 # Go to $HOME directory
  $ cd /test                           # Change to /test directory