Linux Commands cheatsheet for CTF & bug hunting

commands.sh

These are all the useful commands I can think of right now that you don't need
to have root privileges to run.  Some will be useful for Werewolves, others
might be useful for CtF contests, for the rest, who knows.

The five most important commands in Linux are:
apropos           - search the manual page names and descriptions
help              - bash built-in commands, see bash
info              - readable online documentation
man               - an interface to the on-line reference manuals
whatis            - display manual page descriptions

For logging in, logging out, managing a terminal, editing text files:
clear             - clear the terminal screen
exit              - exit from a session
history           - see your command history 
scp               - secure copy (remote file copy program)
screen            - screen manager with VT100/ANSI terminal emulation
sftp              - secure file transfer program
sleep             - delay for a specified amount of time
ssh               - OpenSSH SSH client (remote login program)
vim               - Vi IMproved, a programmers text editor
watch             - execute a program periodically, showing output fullscreen

For dealing with files and directories:
cd                - change directories
chown             - change file owner and group
chgrp             - change group ownership
chmod             - change file mode bits, e.g., such as permissions
cksum             - checksum and count the bytes in a file
cmp               - compare two files byte by byte
cp                - copy files and directories
dd                - convert and copy a file
diff              - compare files line by line
dirname           - strip last component from file name
file              - determine file type
find              - search for files in a directory hierarchy
hexdump           - display file contents in ascii, decimal, hexadecimal, ...
ls                - list directory contents
md5sum            - compute and check MD5 message digest
mkdir             - make directories
mv                - move (rename) files
pwd               - print name of current/working directory
rm                - remove files or directories
rmdir             - remove empty directories
sha1sum           - compute and check SHA1 message digest
stat              - display file or file system status
touch             - change file timestamps
wget              - The non-interactive network downloader

Commands for finding and interacting with other users:
finger            - See some baisc user info, like that last login time
groups            - print the groups a user is in
id                - print real and effective user and group IDs
sslpasswd (1ssl)  - compute password hashes
passwd            - update user's authentication tokens
users             - print the user names of users currently logged in
w                 - Show who is logged on and what they are doing
who               - show who is logged on
whoami            - print effective userid
write             - send a message to another user

Commands for processes and understanding what's going on in the system:
free              - Display amount of free and used memory in the system
kill              - terminate a process
killall           - kill processes by name
ps                - report a snapshot of the current processes.
pstree            - display a tree of processes
top               - display Linux processes

Networking commands:
host              - DNS lookup utility
hostname          - show or set the system's host name
ifconfig          - configure a network interface
mtr               - slightly fancy combination of traceroute and ping
netstat           - Print network connections, routing tables, etc.
ping              - send ICMP ECHO_REQUEST to network hosts
traceroute        - print the route packets trace to network host
dig               - DNS lookup utility

Some advanced stuff for bash scripting and playing Werewolves:
done              - built-in for bash scripting
for               - built-in for bash scripting 
fuser             - identify processes using files or sockets
lsof              - list open files
nohup             - run a command immune to hangups, with output to a non-tty
nslookup          - query Internet name servers interactively
while             - built-in for bash scripting

Commands for I/O processing
awk               - pattern scanning and processing language
cat               - concatenate files and print on the standard output
echo              - display a line of text
grep              - print lines matching a pattern
head              - output the first part of files
HEAD              - Simple command line user agent
less              - opposite of more
more              - file perusal filter for crt viewing
rev               - reverse lines of a file or files
sed               - stream editor for filtering and transforming text
sort              - sort lines of text files
strings           - print the strings of printable characters in files
tail              - output the last part of files
tee               - read from standard input and write to standard output
tr                - translate or delete characters
uniq              - report or omit repeated lines


Others:
alias             - bash built-in commands, see bash
arp               - manipulate the system ARP cache
arping            - send ARP REQUEST to a neighbour host
basename          - strip directory and suffix from filenames
bash              - GNU Bourne-Again SHell
bg                - bash built-in commands, see bash
break             - bash built-in commands, see bash
bzip2             - a block-sorting file compressor, v1.0.6
cal               - display a calendar
comm              - compare two sorted files line by line
convert           - Might be useful for CtF
chaosreader       - Might be useful for CtF
cut               - remove sections from each line of files
date              - print or set the system date and time
dc                - an arbitrary precision calculator
df                - report file system disk space usage
dirs              - bash built-in commands, see bash
dmesg             - print or control the kernel ring buffer
du                - estimate file space usage
egrep             - print lines matching a pattern
eject             - eject removable media
env               - run a program in a modified environment
expect            - Might be useful for CtF
expand            - convert tabs to spaces
export            - bash built-in commands, see bash
false             - do nothing, unsuccessfully
fg                - bash built-in commands, see bash
fgrep             - print lines matching a pattern
fmt               - simple optimal text formatter
gawk              - pattern scanning and processing language
gdb               - The GNU Debugger
gunzip            - compress or expand files
gzip              - compress or expand files
iconv             - Might be useful for CtF
iftop             - Might be useful for CtF
jobs              - bash built-in commands, see bash
join              - join lines of two files on a common field
ln                - make links between files
locate            - find files by name
logname           - print user's login name
logout            - bash built-in commands, see bash
look              - display lines beginning with a given string
ltrace            - Might be useful for CtF
mkfifo            - make FIFOs (named pipes)
mmv               - massive move
mogrify           - Might be useful for CtF
nice              - run a program with modified scheduling priority
nl                - number lines of files
nm                - list symbols from object files
objdump           - display information from object files.
od                - dump files in octal and other formats
paste             - merge lines of files
pax               - Might be useful for CtF
pkill             - look up or signal processes based on name and other at...
popd              - bash built-in commands, see bash
pushd             - bash built-in commands, see bash
pv                - Might be useful for CtF
quota             - get disk quota info
readelf           - Displays information about ELF files.
rename            - rename files
renice            - alter priority of running processes
ripole            - Might be useful for CtF
sdel              - secure delete
select            - Might be useful for CtF
seq               - print a sequence of numbers
shred             - overwrite a file to hide its contents, and optionally ...
shuf              - generate random permutations
split             - split a file into pieces
strace            - Might be useful for CtF
su                - run a command with substitute user and group ID
sudo              - execute a command as another user
sum               - checksum and count the blocks in a file
suspend           - bash built-in commands, see bash
tac               - concatenate and print files in reverse
tar               - an archiver tool
tar               - format of tape archive files
tcpdump           - dump traffic on a network
tcpflow           - Might be useful for CtF
tcpick            - Might be useful for CtF
time              - time a process
timeout           - run a command with a time limit
times             - bash built-in commands, see bash
tshark            - Might be useful for CtF
tsort             - perform topological sort
tty               - print the file name of the terminal connected to stdout
type              - bash built-in commands, see bash
ulimit            - bash built-in commands, see bash
umask             - bash built-in commands, see bash
uname             - print system information
unzip             - list, test and extract compressed files in a ZIP archive
uptime            - Tell how long the system has been running.
uuencode          - Might be useful for CtF
uudecode          - Might be useful for CtF
valgrind          - Might be useful for CtF
wait              - bash built-in commands, see bash
wc                - print newline, word, and byte counts for each file
whereis           - locate binary, source, and manual page files
which             - shows the full path of (shell) commands
whois             - Might be useful for CtF
wireshark         - Might be useful for CtF
zip               - package and compress (archive) files
zipinfo           - list detailed information about a ZIP archive