- 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)
- 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)
- 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
- 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
- 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
- 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)
- 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)
- 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)
- 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
- 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
- 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
- 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