Linux Commands Cheat Sheet

A collection of hopefully useful Linux Commands for pen testers, this is not a complete list but a collection of commonly used commands + syntax as a sort of “cheatsheet”, this content will be constantly updated as I discover new awesomeness.

Linux Penetration Testing Commands

Linux Network Commands

Command Description
netstat -tulpn Show Linux network ports with process ID’s (PIDs)
watch ss -stplu Watch TCP, UDP open ports in real time with socket summary.
lsof -i Show established connections.
macchanger -m MACADDR INTR Change MAC address on KALI Linux.
ifconfig eth0 192.168.2.1/24 Set IP address in Linux.
ifconfig eth0:1 192.168.2.3/24 Add IP address to existing network interface in Linux.
ifconfig eth0 hw ether MACADDR Change MAC address in Linux using ifconfig.
ifconfig eth0 mtu 1500 Change MTU size Linux using ifconfig, change 1500 to your desired MTU.
dig -x 192.168.1.1 Dig reverse lookup on an IP address.
host 192.168.1.1 Reverse lookup on an IP address, in case dig is not installed.
dig @192.168.2.2 domain.com -t AXFR Perform a DNS zone transfer using dig.
host -l domain.com nameserver Perform a DNS zone transfer using host.
nbtstat -A x.x.x.x Get hostname for IP address.
ip addr add 192.168.2.22/24 dev eth0 Adds a hidden IP address to Linux, does not show up when performing an ifconfig.
tcpkill -9 host google.com Blocks access to google.com from the host machine.
echo "1" > /proc/sys/net/ipv4/ip_forward Enables IP forwarding, turns Linux box into a router – handy for routing traffic through a box.
echo "8.8.8.8" > /etc/resolv.conf Use Google DNS.

System Information Commands

Useful for local enumeration.

Command Description
whoami Shows currently logged in user on Linux.
id Shows currently logged in user and groups for the user.
last Shows last logged in users.
mount Show mounted drives.
df -h Shows disk usage in human readable output.
echo "user:passwd" | chpasswd Reset password in one line.
getent passwd List users on Linux.
strings /usr/local/bin/blah Shows contents of none text files, e.g. whats in a binary.
uname -ar Shows running kernel version.
PATH=$PATH:/my/new-path Add a new PATH, handy for local FS manipulation.
history Show bash history, commands the user has entered previously.

Redhat / CentOS / RPM Based Distros

Command Description
cat /etc/redhat-release Shows Redhat / CentOS version number.
rpm -qa List all installed RPM’s on an RPM based Linux distro.
rpm -q --changelog openvpn Check installed RPM is patched against CVE, grep the output for CVE.

YUM Commands

Package manager used by RPM based systems, you can pull some usefull information about installed packages and or install additional tools.

Command Description
yum update Update all RPM packages with YUM, also shows whats out of date.
yum update httpd Update individual packages, in this example HTTPD (Apache).
yum install package Install a package using YUM.
yum --exclude=package kernel* update Exclude a package from being updates with YUM.
yum remove package Remove package with YUM.
yum erase package Remove package with YUM.
yum list package Lists info about yum package.
yum provides httpd What a packages does, e.g Apache HTTPD Server.
yum info httpd Shows package info, architecture, version etc.
yum localinstall blah.rpm Use YUM to install local RPM, settles deps from repo.
yum deplist package Shows deps for a package.
yum list installed | more List all installed packages.
yum grouplist | more Show all YUM groups.
yum groupinstall 'Development Tools' Install YUM group.

Debian / Ubuntu / .deb Based Distros

Command Description
cat /etc/debian_version Shows Debian version number.
cat /etc/*-release Shows Ubuntu version number.
dpkg -l List all installed packages on Debian / .deb based Linux distro.

Linux User Management

Command Description
useradd new-user Creates a new Linux user.
passwd username Reset Linux user password, enter just passwd if you are root.
deluser username Remove a Linux user.

Linux Decompression Commands

How to extract various archives (tar, zip, gzip, bzip2 etc) on Linux and some other tricks for searching inside of archives etc.

Command Description
unzip archive.zip Extracts zip file on Linux.
zipgrep *.txt archive.zip Search inside a .zip archive.
tar xf archive.tar Extract tar file Linux.
tar xvzf archive.tar.gz Extract a tar.gz file Linux.
tar xjf archive.tar.bz2 Extract a tar.bz2 file Linux.
tar ztvf file.tar.gz | grep blah Search inside a tar.gz file.
gzip -d archive.gz Extract a gzip file Linux.
zcat archive.gz Read a gz file Linux without decompressing.
zless archive.gz Same function as the less command for .gz archives.
zgrep 'blah' /var/log/maillog*.gz Search inside .gz archives on Linux, search inside of compressed log files.
vim file.txt.gz Use vim to read .txt.gz files (my personal favorite).
upx -9 -o output.exe input.exe UPX compress .exe file Linux.

Linux Compression Commands

Command Description
zip -r file.zip /dir/* Creates a .zip file on Linux.
tar cf archive.tar files Creates a tar file on Linux.
tar czf archive.tar.gz files Creates a tar.gz file on Linux.
tar cjf archive.tar.bz2 files Creates a tar.bz2 file on Linux.
gzip file Creates a file.gz file on Linux.

Linux File Commands

Command Description
df -h blah Display size of file / dir Linux.
diff file1 file2 Compare / Show differences between two files on Linux.
md5sum file Generate MD5SUM Linux.
md5sum -c blah.iso.md5 Check file against MD5SUM on Linux, assuming both file and .md5 are in the same dir.
file blah Find out the type of file on Linux, also displays if file is 32 or 64 bit.
dos2unix Convert Windows line endings to Unix / Linux.
base64 < input-file > output-file Base64 encodes input file and outputs a Base64 encoded file called output-file.
base64 -d < input-file > output-file Base64 decodes input file and outputs a Base64 decoded file called output-file.
touch -r ref-file new-file Creates a new file using the timestamp data from the reference file, drop the -r to simply create a file.
rm -rf Remove files and directories without prompting for confirmation.

Samba Commands

Connect to a Samba share from Linux.

$ smbmount //server/share /mnt/win -o user=username,password=password1
$ smbclient -U user \\\\server\\share
$ mount -t cifs -o username=user,password=password //x.x.x.x/share /mnt/share

Breaking Out of Limited Shells

Credit to G0tmi1k for these (or wherever he stole them from!).

The Python trick:

python -c 'import pty;pty.spawn("/bin/bash")'
echo os.system('/bin/bash')
/bin/sh -i

Misc Commands

Command Description
init 6 Reboot Linux from the command line.
gcc -o output.c input.c Compile C code.
gcc -m32 -o output.c input.c Cross compile C code, compile 32 bit binary on 64 bit Linux.
unset HISTORYFILE Disable bash history logging.
rdesktop X.X.X.X Connect to RDP server from Linux.
kill -9 $$ Kill current session.
chown user:group blah Change owner of file or dir.
chown -R user:group blah Change owner of file or dir and all underlying files / dirs – recersive chown.
chmod 600 file Change file / dir permissions, see [Linux File System Permissons](#linux-file-system-permissions) for details.

Clear bash history:

      $ ssh user@X.X.X.X | cat /dev/null > ~/.bash_history
    

Linux File System Permissions

Value Meaning
777 rwxrwxrwx No restriction, global WRX any user can do anything.
755 rwxr-xr-x Owner has full access, others can read and execute the file.
700 rwx------ Owner has full access, no one else has access.
666 rw-rw-rw- All users can read and write but not execute.
644 rw-r--r-- Owner can read and write, everyone else can read.
600 rw------- Owner can read and write, everyone else has no access.

Linux File System

Directory Description
/ / also know as “slash” or the root.
/bin Common programs, shared by the system, the system administrator and the users.
/boot Boot files, boot loader (grub), kernels, vmlinuz
/dev Contains references to system devices, files with special properties.
/etc Important system config files.
/home Home directories for system users.
/lib Library files, includes files for all kinds of programs needed by the system and the users.
/lost+found Files that were saved during failures are here.
/mnt Standard mount point for external file systems.
/media Mount point for external file systems (on some distros).
/net Standard mount point for entire remote file systems – nfs.
/opt Typically contains extra and third party software.
/proc A virtual file system containing information about system resources.
/root root users home dir.
/sbin Programs for use by the system and the system administrator.
/tmp Temporary space for use by the system, cleaned upon reboot.
/usr Programs, libraries, documentation etc. for all user-related programs.
/var Storage for all variable files and temporary files created by users, such as log files, mail queue, print spooler. Web servers, Databases etc.

Linux Interesting Files / Dir’s

Places that are worth a look if you are attempting to privilege escalate / perform post exploitation.

Directory Description
/etc/passwd Contains local Linux users.
/etc/shadow Contains local account password hashes.
/etc/group Contains local account groups.
/etc/init.d/ Contains service init script – worth a look to see whats installed.
/etc/hostname System hostname.
/etc/network/interfaces Network interfaces.
/etc/resolv.conf System DNS servers.
/etc/profile System environment variables.
~/.ssh/ SSH keys.
~/.bash_history Users bash history log.
/var/log/ Linux system log files are typically stored here.
/var/adm/ UNIX system log files are typically stored here.
/var/log/apache2/access.log

/var/log/httpd/access.log

Apache access log file typical path.
/etc/fstab File system mounts.
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