Unix is now one of the most commonly used Operating systems used for various purposes such as Personal use, Servers, Smartphones, and many more. It was developed in the 1970’s at AT& T Labs by two famous personalities Dennis M. Ritchie and Ken Thompson.
- Kernel
- System Library
- Shell
- Hardware Layer
- System Utility
ls # list all files
ls -al # lists hidden files
cd <path> # change directory to path
cd # change to home
pwd # shows current directory
mkdir <dirName> # create a new directory with given name
cat <fileName> # displays the file content
cat > <fileName> # creates a new file
rm <fileName> # removes file with given name
du -sh * # list directories with their total sizes
df -h # to see free disk space
ls -l # to show file type and access permission
r # read permission (4)
w # write permission (2)
x # execute permission (1)
chown <user> # for changing the ownership of a file/directory
chown <user>: <group> <fileName> # change the user as well as group for a file or directory
chmod <mode> <filename> # change the permissions of a file/directory
chmod +rwx #filename to add permissions.
chmod -rwx #directoryname to remove permissions.
chmod +x #filename to allow executable permissions.
chmod -wx #filename to take out write and executable permissions.- Use the tar command to compress and expand files from the command line. The syntax is shown below:
- tar [options] [archive-file] [file or directory to be archived]
tar -zcvf foo.txt.tar.gz foo.txt # Create a zipped archive-file
tar -tvf foo.txt.tar.gz # List archive files
tar -xvf foo.txt.tar.gz # Extracting archive-file
Options:
-c # Creates Archive
-x # Extract the archive
-f # creates archive with given filename
-t # displays or lists files in archived file
-u # archives and adds to an existing archive file
-v # Displays Verbose Information
-A # Concatenates the archive files
-z # zip, tells tar command that creates tar file using gzip
-j # filter archive tar file using tbzip
-W # Verify a archive file
-r # update or add file or directory in already existed .tar file- To compress a file , zip command is use. The syntax is shown below:
### Syntax
- zip [options] [archive-file] [file or directory to be archived]
Options:
–d # Remove a specific file from zip
-m # Deletes the original files after zipping
-r # recursively zip from a folder
-u # Add new file in zip
-v # Show files in zip - Linux networking commands are widely used to analyze, maintain & troubleshoot the network(s) connected to that system
**Command** **Functionality**
- ping [ip_addr/hostname] # check the connectivity between the 2 devices(host/server)
- ifconfig [options] [interface] # configure the kernel-resident network interfaces
- ip [options] OBJECT {COMMAND | help} # to show/manipulate routing, devices and tunnels
- traceroute [options] host_address [pathlength] # displays the route a packet takes to reach destination
- netstat [options] # monitoring incoming & outgoing network connections
- ss [options] [filter] # used to dump socket statistics
- dig [server] [name] [type] # retrieve information about DNS name servers
- nslookup [options] # retrieve information from DNS name server/used to DNS lookup
- arp [-v] [-i if] [-H type] -a [hostname] # displays the ARP(Address Resolution Protocol) cache
- curl [options] [URL] # transfer data to or from a server using various protocol
- wget [options] [URL] # used to download files from the server without being logged on
- tcpdump [options] [interface] # capture and analyze the incoming & outgoing packets
- host [-aCdlriTWV] [-c class] [-N ndots] [-t type]
[-W time] [-R number] [-m flag] hostname [server] # used to find the IP address from hostname or vice-versa
- hostname -[options] [file] # obtain the DNS name and set the system's hostname/NIS domain name
- whois [hostname] # displays who is the owner of the domain and more info
- Process commands in linux are used to manage the processes running on the system. There syntaxes and descriptions are listed below.
Commands Description
- top # Used to get the details of all active processes
- bg # Send a process to the background
- fg # To bring a stopped process in the foreground & run
- ps # List all running processes for a user with appropriate permissions
- ps <PID> # Displays the status of the process with PID <PID>
- pidof # Returns the PID of a particular process
- kill <PID> # Kill the process with PID <PID>
- nice # Execute a process with modified scheduling priority
- renice # Modify priority of a group of processes
- df # Displays the disk space available on the filesystem with each filename's argument
- free [option] # Summary of RAM usage, including total, used, free, shared & available memory and swap space