Common useful Linux Terminal Commands

gistfile1.sh

# 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 now in deprecated network command)
# 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