Linux means the kernel of the system where it is central to control everything on a PC. Linux is a combination of software, called GNU / Linux, which defines the operating system.
GNU is the free software that provides open source equivalents of many common UNIX commands.
The Linux part of this combination is the Linux kernel, which is the core of the operating system.
The story of Linux begins with UNIX, an operating system developed at AT&T Bell Labs in the 1970s.
UNIX is written in C programming language.
Linux was written in C and Assembly language.
Linux started back in 1991 as a hobby project by Linus Torvalds who has studied in Helsinki, Finland at the University of Helsinki. Linux is Open-Source so that means everyone can use it, see source code and make changes.
Linus made the source programming code (the instructions a computer uses to operate) freely available, allowing others to participate and shape this new operating system.
Lots of hackers. especially ethical hackers use linux with python because python can import some tools that exist in the system and use them to make very advanced scripts. Python is also very easy to learn and it gives good performance.
Free and Open Source Software (FOSS) - refer to a software where the copy-right has been given up, so everyone is allowed to view source code and make changes. That's what Linus Torvalds has done with Linux even though he has created Linux he can't ban a person because Linus has given up rights with GPLv2 license.
Free/Libre and Open Source Software (FLOSS) - a researcher studying practices and methods used by developers in the free software community decided that these questions were independent of the developers' political views, so he used the term “FLOSS,” meaning “Free/Libre and Open Source Software,” to explicitly avoid a preference between the two political camps
BSD stands for "Berkeley Software Distribution". It is the distribution name of the source code from the University of California, Berkeley which has been used as an extension to AT & T's Research UNIX operating system.
Linux is a group of free open source operating systems built around Linux Kernel, which is like the UNIX operating system. It belongs to UNIX just like family operating systems. It was packaged as Linux distribution to distribute for both server and desktop purposes. BSD (Berkeley Software Distribution) is derived from the UNIX operating system, which was purely written in programming language C. It belongs to the UNIX operating system family. The core type of the BSD operating system is monolithic. The default user interface in BSD is the command line user interface.
| Linux | BSD | |
|---|---|---|
| License | It is licensed under the General Public License (GPL). | It is licensed under the BSD License which is much less restrictive.fun?' |
| Development | Developed by the developer community. | Developed by the University of California, Berkeley. |
| Control | Mostly controlled by Linus Torvalds. | Not controlled. |
| OS | Concentrates mostly on kernel development. | Concentrates completely on an OS. |
| Base system | It is a group of many small 'sub systems'. | It has a base system that supports the entire operating system. |
| Upgrade | Difficult to upgrade and requires package management etc. | Easy to upgrade. |
| Hardware support | Supports all types of hardware for a short time. | Takes longer to support all types of hardware. |
| Copy-left | Have a copy-left. | No copy-left. |
Software that runs on a computer device and manages the hardware and software components that make up the system. Commonly abbreviated as OS.
The users today will choose from among 3 major operating systems which are Microsoft Windows, Apple macOS, Linux. Only Microsoft Windows is based on proprietary code that is not Unix or Linux based.
Typical format for command is:
command [options] [arguments]
System
| uname -a | --- | Display linux system infomartion |
| uname -r | --- | Display kernel release information |
| uptime | --- | Show how long the system has been running + load |
| hostname | --- | Show system host name |
| hostname -i | --- | Display the IP address of the host |
| last reboot | --- | Show system reboot history |
| date | --- | Show the current date and time |
| cal | --- | Show the month calendar |
| w | --- | Display who is online |
| whoami | --- | Who you are logged in as |
| finger user | --- | Display information about user |
Hardware
| dmesg | --- | Detected hardware and boot messages |
| 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 |
| free -m | --- | Used and free memory (-m for MB) |
| lspci -tv | --- | Show PCI devices |
| lsusb -tv | --- | Show USB devices |
| dmidecode | --- | Show hardware info from the BIOS |
| 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 |
Users
| id | --- | Show the active user id with login and group |
| last | --- | Show last logins on the system |
| who | --- | Show who is logged on the system |
| groupadd admin | --- | Add group "admin" |
| useradd –c "Robert" | --- | g admin –m sam #Create user "rob" |
| userdel rob | --- | Delete user rob |
| adduser rob | --- | Add user "rob" |
| usermod | --- | Modify user information |
File commands
| ls -al | --- | Display all information about files/ directories |
| pwd | --- | Show the path of current directory |
| mkdir directory-name | --- | Create a directory |
| rm file-name | --- | Delete file |
| rm -r directory-name | --- | Delete directory recursively |
| rm -r file-name | --- | Forcefully remove file |
| rm -rf directory-name | --- | Forcefully remove directory recursively |
| cp file1 file2 | --- | Copy file1 to file2 |
| cp -r dir1 dir2 | --- | Copy dir1 to dir2, create dir2 if it doesn't exist |
| mv file1 file2 | --- | Rename source to dest / move source to directory |
| ln -s /path/to/file-name link-name | --- | Create symbolic link to file-name |
| touch file | --- | Create or update file |
| cat > file | --- | Place standart input into file |
| more file | --- | Output contents of file |
| head file | --- | Output contents of file |
| tail file | --- | Output last 10 lines of file |
| tail -f file | --- | Output contents of file as it grows starting with the last 10 lines |
| gpg -c file | --- | Encrypt file |
| gpg file.gpg | --- | Decrypt file |
| wc | --- | Print the number of bytes, words, and lines in files |
| xargs | --- | Execute command lines from standart input |
Process related
| ps | --- | Display your currently active processes |
| ps aux / grep 'telnet' | --- | Find all process id related to telnet process |
| pmap | --- | Memory map of process |
| top | --- | Display all running processes |
| kill pid | --- | Kill process with mentioned pid id |
| killall proc | --- | Kill all processes named proc |
| pkill process-name | --- | Send signal to a process with its name |
| bg | --- | Resumes suspended jobs without bringing them to foreground |
| 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 |
| chmod 777 /data/test.c | --- | Set rwx permission for owner, group, 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 owner-user:owner-group file-name | --- | Change owner of the file |
| chown owner-user:owner-group file-name | --- | chown owner-user:owner-group directory |
Network
| ip addr show | --- | Display all network interfaces and ip address |
| ip address add 192.168.0.1 dev eth0 | --- | Set ip address |
| ethtool eth0 | --- | Linux tool to show ethernet status |
| mii-tool eth0 | --- | Linux tool to show ethernet status |
| ping host | --- | Send echo request to test connection |
| whois domain | --- | Get who is information for domain |
| dig domain | --- | Get DNS information for domain |
| dig -x host | --- | Reverse lookup host |
| host google.com | --- | Lookup DNS ip address for the name |
| hostname -i | --- | Lookup local ip address |
| wget file | --- | Download file |
| netstat -tupl | --- | Listing all active listening ports |
Compression / archives
| tar cf home.tar home | --- | Create tar named home.tar containing home/ |
| 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 |
Install package
| rpm -i pkgname.rpm | --- | Install rpm based package |
| rpm -e pkgname | --- | Remove package |
Install from source
| ./configure | --- | |
| make | --- | |
| make install | --- |
Search
| grep pattern files | --- | Search for pattern in files |
| grep -r pattern dir | --- | Search recursively for pattern in dir |
| locate file | --- | Find all instaces of file |
| find /home/rob -name 'index'* | --- | Find files names that start with "index" |
| find /home -size +10000k | --- | Find files larger than 10000k in /home |
Login (SSH and TELNET)
| ssh user@host | --- | Connect to host as user |
| 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 rsync |
| rsync -a /home/apps /backup/ | --- | Synchronize source to destination |
Disk usage
| df -h | --- | Show free space on mounted filesystems |
| df -i | --- | Show free inodes on mounted filesystems |
| fdisk -l | --- | Show disks partitions sizes and types |
| du -ah | --- | Display disk usage in human readable form |
| du -sh | --- | Display total disk usage on the current directory |
| findmnt | --- | Displays target mount point for all filesystem |
| mount device-path mount-point | --- | Mount device |
Directory traverse
| cd .. | --- | To go up one level of the directory tree |
| cd | --- | Go to $HOME directory |
| cd /test | --- | Change to /test directory |
A pair of single quotes ( ' ) will prevent the shell from interpreting any metacharacter.
The semicolon (;) can be used to separate multiple commands to be executed in order.
To execute the same command as previously executed five commands ago, you would type: !-5
HOME is an example of an environment variable.
The command that can report the location of a command: which
The history command will print a list of the commands that you've previously executed.
The environment variable that contains a list of directories that is searched for commands to execute is 'PATH'
To search the man page sections for the keyword example, which of the following you can execute 'man –k example' and 'apropos example'
The following sections commonly appear on a man page: DESCRIPTION, NAME, SYNOPSIS
To start searching a man page, the first key you press is: /
To exit the info page, press: Q
Commands typically executed by a user are covered in section 1 of the manual.
If you are reading the synopsis of a command from a man page, then items in square brackets are: Optional
The info page is like a guide; a man page is a more concise reference.
Section 9 of man pages relates to Kernel routines