Linux basic commands:
Directory Traverse commands:
cd .. # Move up one level in the directory tree structure
cd # Change directory to $HOME directory
cd /test # Change directory to /test directory
mkdir test # Create a directory test
rmdir test # Removes directory test
Basic Commands:
pwd # Prints current working directory
| # Pipe (redirect) output
sudo [command] # run <command> in superuser mode
man [command] # display help pages of <command>
[command]& # run <command> in the background
>> [fileA] # append to fileA, preserving existing contents
> [fileA] # output to fileA, overwriting contents
echo -n # display a line of text
xargs # build command line from previous output
1>2& # Redirect stdout to stderr
ctrl-z # Suspend current task
> # This notation is used to redirect stdout to a file.
2> # This notation will redirect stderr to a file
&> # This notation will redirect both stdout and stderr.
File Commands:
ls -al # Lists files - both regular & hidden files and their permissions as well.
pwd # Displays the current directory file path
mkdir ‘directory_name’ # Creates a new directory
rm file_name # Removes a file
rm -f filename # Forcefully removes a file
rm -r directory_name # Removes a directory recursively
rm -rf directory_name # Removes a directory forcefully and recursively
cp file1 file2 # Copies the contents of file1 to file2
cp -r dir1 dir2 # Recursively Copies dir1 to dir2. dir2 is created if it does not exist
mv file1 file2 # Renames file1 to file2
ln -s /path/to/file_name link_name # Creates a symbolic link to file_name
touch file_name # Creates a new file
cat > file_name # Places standard input into a file
more file_name # Outputs the contents of a file
less file_name # Outputs the contents of a file one page at a time.
head file_name # Displays the first 10 lines of a file
tail file_name # Displays the last 10 lines of a file
tail -f file_name # Displays last part of the file or running logs.
gpg -c file_name # Encrypts a file
gpg file_name.gpg # Decrypts a file
wc # Prints the number of bytes, words and lines in a file
xargs # Executes commands from standard input
split -l file # Split file into pieces
head -n file # output the "n" no of lines from the starting of the file
Process Related commands:
ps # Display currently active processes
ps aux | grep ‘telnet’ # Searches for the id of the process ‘telnet’
pmap # Displays memory map of processes
top # Displays all running processes
kill pid # Terminates process with a given pid
killall proc # Kills / Terminates all processes named proc
pkill process-name # Sends a signal to a process with its name
bg # Resumes suspended jobs in the background
fg # Brings suspended jobs to the foreground
fg n # Brings job n to the foreground
lsof # Lists files that are open by processes
renice 19 PID # Makes a process run with very low priority
pgrep firefox # Find Firefox process ID
pstree # Visualizing processes in tree model
free -m # displays free and used system memory
dmesg -k # display system messages
service [start|stop|restart] # manage or run sysV init scritp
File Permission commands:
ls -l filename.txt
-rw-r--r-- 12 linuxize users 12.0K Apr 8 20:51 filename.txt
|[-][-][-]- [------] [---]
| | | | | | |
| | | | | | +-------------------> 7. Group
| | | | | +-------------------------> 6. Owner
| | | | +------------------------------> 5. Alternate Access Method
| | | +-------------------------------> 4. Others Permissions
| | +---------------------------------> 3. Group Permissions
| +-----------------------------------> 2. Owner Permissions
+------------------------------------> 1. File Type
Each write, read, and execute permissions have the following number value:
r (read) = 4
w (write) = 2
x (execute) = 1
no permissions = 0
The permissions number of a specific user class is represented by the sum of the values of the permissions for that group.
Ex:
Owner: rwx=4+2+1=7
Group: r-x=4+0+1=5
Others: r-x=4+0+0=4
chmod octal filename # Change file permissions of the file to octal
Example
chmod 777 /data/test.c # Set rwx permissions to owner, group and everyone (everyone else who has access to the server)
chmod 755 /data/test.c # Set rwx to the owner and r_x to group and everyone
chmod 766 /data/test.c # Sets rwx for owner, rw for group and everyone
chown owner user-file # Change ownership of the file
chown owneruser:owner-group file_name # Change owner and group owner of the file
chown owneruser:owner-group directory # Change owner and group owner of the directory
Compression / Archives commands:
tar -cf test.tar test # Creates archive file called ‘home.tar’ from file ‘test’
tar -xf files.tar # Extract archive file ‘files.tar’
tar -zcvf home.tar.gz source-folder # Creates gzipped tar archive file from source folder
gzip file # Compression a file with .gz extension
gunzip file.gz # Uncompress the .gz file
Install Packages commands:
rpm -i pkg_name.rpm # Install an rpm package
rpm -e pkg_name # Removes an rpm package
dnf install pkg_name # Install package using dnf utility
Search commands:
grep ‘pattern’ files # Search for a given pattern in files
grep -r pattern dir # Search recursively for a pattern in a given directory
locate file # Find all instances of the file
find /home/ -name “index” # Find file names that begin with ‘index’ in /home folder
find /home -size +10000k # Find files greater than 10000k in the home folder
Disk Usage commands:
df -h # Displays free space on mounted systems
df -i # Displays free inodes on filesystems
fdisk -l # Shows disk partitions, sizes, and types
du -sh # Displays disk usage in the current directory in a human-readable format
findmnt # Displays target mount point for all filesystems
mount device-path mount-point # Mount a device
umount mount-point # Unmount a device
Syestem commands:
uname # Displays Linux system information
uname -r # Displays kernel release information
uptime # Displays how long the system has been running including load average
hostname # Shows the system hostname
hostname -i # Displays the IP address of the system
last reboot # Shows system reboot history
date # Displays current system date and time
timedatectl # Query and change the System clock
cal # Displays the current calendar month and day
w # Displays currently logged in users in the system
whoami # Displays who you are logged in as
finger username # Displays information about the user
Hardware commands:
dmesg # Displays bootup messages
cat /proc/cpuinfo # Displays more information about CPU e.g model, model name, cores, vendor id
cat /proc/meminfo # Displays more information about hardware memory e.g. Total and Free memory
lshw # Displays information about system’s hardware configuration
lsblk # Displays block devices related information
free -m # Displays free and used memory in the system (-m flag indicates memory in MB)
lspci -tv # Displays PCI devices in a tree-like diagram
lsusb -tv # Displays USB devices in a tree-like diagram
dmidecode # Displays hardware information from the BIOS
hdparm -i /dev/xda # Displays information about disk data
hdparm -tT /dev/xda # Conducts a read speed test on device xda
badblocks -s /dev/xda # Tests for unreadable blocks on disk
Users commands:
id # Displays the details of the active user e.g. uid, gid, and groups
last # Shows the last logins in the system
who # Shows who is logged in to the system
groupadd “admin” # Adds the group ‘admin’
adduser “Sam” # Adds user Sam
passwd "Sam" # Sets password for Sam.
userdel “Sam” # Deletes user Sam
usermod # Used for changing / modifying user information
Network commands:
ip addr show # Displays IP addresses and all the network interfaces
ip address add 192.168.0.1/24 dev eth0 # Assigns IP address 192.168.0.1 to interface eth0
ifconfig # Displays IP addresses of all network interfaces
ping host # ping command sends an ICMP echo request to establish a connection to server / PC
whois domain # Retrieves more information about a domain name
dig domain # Retrieves DNS information about the domain
dig -x host # Performs reverse lookup on a domain
host google.com # Performs an IP lookup for the domain name
hostname -i # Displays local IP address
wget file_name # Downloads a file from an online source
netstat -pnltu # Displays all active listening ports
netstat -r -v # Displays network information, routing and connections
tcpdump # dump network traffic
Login commands:
ssh user@host # Securely connect to host as user
ssh -p port_number user@host # Securely connect to host using a specified port
ssh host # Securely connect to the system via SSH default port 22
telnet host # Connect to host via telnet default port 23
File Transfer commands:
scp file1.txt server2:/tmp # Securely copy file1.txt to server2 in /tmp directory
rsync -a /home/apps /backup/ # Synchronize contents in /home/apps directory with /backup directory
Crontab commands:
crontab -l # List the cron jobs of the current user.
crontab -e # To edit cron jobs
crontab -r # removes crontab tasks.
crontab -u username -l # to view crontab entries of a specific user.
syntax:
[Minute] [hour] [Day_of_the_Month] [Month_of_the_Year] [Day_of_the_Week] [command]
Ex:
*/5* * * * * /scripts/script.sh # will execute script every 5 minutes.
0 */6 * * * /scripts/script.sh # will execute script every 6 hours.
Tips and Tricks for Using Linux Command Line:
1. You can use the clear command to clear the terminal if it gets filled up with too many commands.
2. TAB can be used to fill up in terminal. For example, You just need to type “cd Doc” and then TAB and the terminal fills the rest up and makes it “cd Documents”.
3. Ctrl+C can be used to stop any command in terminal safely. If it doesn't stop with that, then Ctrl+Z can be used to force-stop it.
4. You can exit from the terminal by using the exit command.
5. You can power off or reboot the computer by using the command sudo halt and sudo reboot.
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