linux工具使用技巧

https://github.com/trimstray/the-book-of-secret-knowledge

Reload shell without exit
exec $SHELL -l
Close shell keeping all subprocess running
disown -a && exit
Exit without saving shell history
kill -9 $$
unset HISTFILE && exit
Perform a branching conditional
true && echo success
false || echo failed
Pipe stdout and stderr to separate commands
some_command > >(/bin/cmd_for_stdout) 2> >(/bin/cmd_for_stderr)
Redirect stdout and stderr each to separate files and print both to the screen
(some_command 2>&1 1>&3 | tee errorlog ) 3>&1 1>&2 | tee stdoutlog
List of commands you use most often
history | \
awk '{CMD[$2]++;count++;}END { for (a in CMD)print CMD[a] " " CMD[a]/count*100 "% " a;}' | \
grep -v "./" | \
column -c3 -s " " -t | \
sort -nr | nl | head -n 20
Sterilize bash history
function sterile() {
history | awk '$2 != "history" { $1=""; print $0 }' | egrep -vi "\
curl\b+.*(-E|--cert)\b+.*\b*|\
curl\b+.*--pass\b+.*\b*|\
curl\b+.*(-U|--proxy-user).*:.*\b*|\
curl\b+.*(-u|--user).*:.*\b*
.*(-H|--header).*(token|auth.*)\b+.*|\
wget\b+.*--.*password\b+.*\b*|\
http.?://.+:.+@.*\
" > $HOME/histbuff; history -r $HOME/histbuff;
}

export PROMPT_COMMAND="sterile"
Quickly backup a file
cp filename{,.orig}
Empty a file (truncate to 0 size)
>filename
Delete all files in a folder that don't match a certain file extension
rm !(*.foo|*.bar|*.baz)
Pass multi-line string to a file
# cat >filename ... - overwrite the file
# cat >>filename ... - append to a file
cat > filename << __EOF__
data data data
__EOF__
Edit a file on a remote host using vim
vim scp://user@host//etc/fstab
Create a directory and change into it at the same time
mkd() { mkdir -p "$@" && cd "$@"; }
Convert uppercase files to lowercase files
rename 'y/A-Z/a-z/' *
Print a row of characters across the terminal
printf "%`tput cols`s" | tr ' ' '#'
Show shell history without line numbers
history | cut -c 8-
fc -l -n 1 | sed 's/^\s*//'
Run command(s) after exit session
cat > /etc/profile << __EOF__
_after_logout() {

username=$(whoami)

for _pid in $(ps afx | grep sshd | grep "$username" | awk '{print $1}') ; do

kill -9 $_pid

done

}
trap _after_logout EXIT
__EOF__
Generate a sequence of numbers
for ((i=1; i<=10; i+=2)) ; do echo $i ; done
# alternative: seq 1 2 10

for ((i=5; i<=10; ++i)) ; do printf '%02d\n' $i ; done
# alternative: seq -w 5 10

for i in {1..10} ; do echo $i ; done
Simple Bash filewatching
unset MAIL; export MAILCHECK=1; export MAILPATH='$FILE_TO_WATCH?$MESSAGE'
Tool: mount
Mount a temporary ram partition
mount -t tmpfs tmpfs /mnt -o size=64M
-t - filesystem type
-o - mount options
Remount a filesystem as read/write
mount -o remount,rw /
Tool: fuser
Show which processes use the files/directories
fuser /var/log/daemon.log
fuser -v /home/supervisor
Kills a process that is locking a file
fuser -ki filename
-i - interactive option
Kills a process that is locking a file with specific signal
fuser -k -HUP filename
--list-signals - list available signal names
Show what PID is listening on specific port
fuser -v 53/udp
Show all processes using the named filesystems or block device
fuser -mv /var/www
Tool: lsof
Show process that use internet connection at the moment
lsof -P -i -n
Show process that use specific port number
lsof -i tcp:443
Lists all listening ports together with the PID of the associated process
lsof -Pan -i tcp -i udp
List all open ports and their owning executables
lsof -i -P | grep -i "listen"
Show all open ports
lsof -Pnl -i
Show open ports (LISTEN)
lsof -Pni4 | grep LISTEN | column -t
List all files opened by a particular command
lsof -c "process"
View user activity per directory
lsof -u username -a +D /etc
Show 10 largest open files
lsof / | \
awk '{ if($7 > 1048576) print $7/1048576 "MB" " " $9 " " $1 }' | \
sort -n -u | tail | column -t
Show current working directory of a process
lsof -p <PID> | grep cwd
Tool: ps
Show a 4-way scrollable process tree with full details
ps awwfux | less -S
Processes per user counter
ps hax -o user | sort | uniq -c | sort -r
Show all processes by name with main header
ps -lfC nginx
Tool: find
Find files that have been modified on your system in the past 60 minutes
find / -mmin 60 -type f
Find all files larger than 20M
find / -type f -size +20M
Find duplicate files (based on MD5 hash)
find -type f -exec md5sum '{}' ';' | sort | uniq --all-repeated=separate -w 33
Change permission only for files
cd /var/www/site && find . -type f -exec chmod 766 {} \;
cd /var/www/site && find . -type f -exec chmod 664 {} +
Change permission only for directories
cd /var/www/site && find . -type d -exec chmod g+x {} \;
cd /var/www/site && find . -type d -exec chmod g+rwx {} +
Find files and directories for specific user
find . -user <username> -print
Find files and directories for all without specific user
find . \!-user <username> -print
Delete older files than 60 days
find . -type f -mtime +60 -delete
Recursively remove all empty sub-directories from a directory
find . -depth -type d -empty -exec rmdir {} \;
How to find all hard links to a file
find </path/to/dir> -xdev -samefile filename
Recursively find the latest modified files
find . -type f -exec stat --format '%Y :%y %n' "{}" \; | sort -nr | cut -d: -f2- | head
Recursively find/replace of a string with sed
find . -not -path '*/\.git*' -type f -print0 | xargs -0 sed -i 's/foo/bar/g'
Recursively find/replace of a string in directories and file names
find . -depth -name '*test*' -execdir bash -c 'mv -v "$1" "${1//foo/bar}"' _ {} \;
Recursively find suid executables
find / \( -perm -4000 -o -perm -2000 \) -type f -exec ls -la {} \;
Tool: top
Use top to monitor only all processes with the specific string
top -p $(pgrep -d , <str>)
<str> - process containing string (eg. nginx, worker)
Tool: vmstat
Show current system utilization (fields in kilobytes)
vmstat 2 20 -t -w
2 - number of times with a defined time interval (delay)
20 - each execution of the command (count)
-t - show timestamp
-w - wide output
-S M - output of the fields in megabytes instead of kilobytes
Show current system utilization will get refreshed every 5 seconds
vmstat 5 -w
Display report a summary of disk operations
vmstat -D
Display report of event counters and memory stats
vmstat -s
Display report about kernel objects stored in slab layer cache
vmstat -m
Tool: iostat
Show information about the CPU usage, and I/O statistics about all the partitions
iostat 2 10 -t -m
2 - number of times with a defined time interval (delay)
10 - each execution of the command (count)
-t - show timestamp
-m - fields in megabytes (-k - in kilobytes, default)
Show information only about the CPU utilization
iostat 2 10 -t -m -c
Show information only about the disk utilization
iostat 2 10 -t -m -d
Show information only about the LVM utilization
iostat -N
Tool: strace
Track with child processes
# 1)
strace -f -p $(pidof glusterfsd)

# 2)
strace -f $(pidof php-fpm | sed 's/\([0-9]*\)/\-p \1/g')
Track process with 30 seconds limit
timeout 30 strace $(< /var/run/zabbix/zabbix_agentd.pid)
Track processes and redirect output to a file
ps auxw | grep '[a]pache' | awk '{print " -p " $2}' | \
xargs strace -o /tmp/strace-apache-proc.out
Track with print time spent in each syscall and limit length of print strings
ps auxw | grep '[i]init_policy' | awk '{print " -p " $2}' | \
xargs strace -f -e trace=network -T -s 10000
Track the open request of a network port
strace -f -e trace=bind nc -l 80
Track the open request of a network port (show TCP/UDP)
strace -f -e trace=network nc -lu 80
Tool: kill
Kill a process running on port
kill -9 $(lsof -i :<port> | awk '{l=$2} END {print l}')
Tool: diff
Compare two directory trees
diff <(cd directory1 && find | sort) <(cd directory2 && find | sort)
Compare output of two commands
diff <(cat /etc/passwd) <(cut -f2 /etc/passwd)
Tool: vimdiff
Highlight the exact differences, based on characters and words
vimdiff file1 file2
Compare two JSON files
vimdiff <(jq -S . A.json) <(jq -S . B.json)
Compare Hex dump
d(){ vimdiff <(f $1) <(f $2);};f(){ hexdump -C $1|cut -d' ' -f3-|tr -s ' ';}; d ~/bin1 ~/bin2
diffchar
Save diffchar @ ~/.vim/plugins

Click F7 to switch between diff modes

Usefull vimdiff commands:

qa to exit all windows
:vertical resize 70 to resize window
set window width Ctrl+W [N columns]+(Shift+)<\>
Tool: tail
Annotate tail -f with timestamps
tail -f file | while read ; do echo "$(date +%T.%N) $REPLY" ; done
Analyse an Apache access log for the most common IP addresses
tail -10000 access_log | awk '{print $1}' | sort | uniq -c | sort -n | tail
Analyse web server log and show only 5xx http codes
tail -n 100 -f /path/to/logfile | grep "HTTP/[1-2].[0-1]\" [5]"
Tool: tar
System backup with exclude specific directories
cd /
tar -czvpf /mnt/system$(date +%d%m%Y%s).tgz --directory=/ \
--exclude=proc/* --exclude=sys/* --exclude=dev/* --exclude=mnt/* .
System backup with exclude specific directories (pigz)
cd /
tar cvpf /backup/snapshot-$(date +%d%m%Y%s).tgz --directory=/ \
--exclude=proc/* --exclude=sys/* --exclude=dev/* \
--exclude=mnt/* --exclude=tmp/* --use-compress-program=pigz .
Tool: dump
System backup to file
dump -y -u -f /backup/system$(date +%d%m%Y%s).lzo /
Restore system from lzo file
cd /
restore -rf /backup/system$(date +%d%m%Y%s).lzo
Tool: cpulimit
Limit the cpu usage of a process
cpulimit -p pid -l 50
Tool: pwdx
Show current working directory of a process
pwdx <pid>
Tool: taskset
Start a command on only one CPU core
taskset -c 0 <command>
Tool: tr
Show directories in the PATH, one per line
tr : '\n' <<<$PATH
Tool: chmod
Remove executable bit from all files in the current directory
chmod -R -x+X *
Restore permission for /bin/chmod
# 1:
cp /bin/ls chmod.01
cp /bin/chmod chmod.01
./chmod.01 700 file

# 2:
/bin/busybox chmod 0700 /bin/chmod

# 3:
setfacl --set u::rwx,g::---,o::--- /bin/chmod
Tool: who
Find last reboot time
who -b
Detect a user sudo-su'd into the current shell
[[ $(who -m | awk '{ print $1 }') == $(whoami) ]] || echo "You are su-ed to $(whoami)"
Tool: last
Was the last reboot a panic?
(last -x -f $(ls -1t /var/log/wtmp* | head -2 | tail -1); last -x -f /var/log/wtmp) | \
grep -A1 reboot | head -2 | grep -q shutdown && echo "Expected reboot" || echo "Panic reboot"
Tool: screen
Start screen in detached mode
screen -d -m <command>
Attach to an existing screen session
screen -r -d <pid>
Tool: script
Record and replay terminal session
### Record session
# 1)
script -t 2>~/session.time -a ~/session.log

# 2)
script --timing=session.time session.log

### Replay session
scriptreplay --timing=session.time session.log
Tool: du
Show 20 biggest directories with 'K M G'
du | \
sort -r -n | \
awk '{split("K M G",v); s=1; while($1>1024){$1/=1024; s++} print int($1)" "v[s]"\t"$2}' | \
head -n 20
Tool: inotifywait
Init tool everytime a file in a directory is modified
while true ; do inotifywait -r -e MODIFY dir/ && ls dir/ ; done;
Tool: openssl
Testing connection to the remote host
echo | openssl s_client -connect google.com:443 -showcerts
Testing connection to the remote host (with SNI support)
echo | openssl s_client -showcerts -servername google.com -connect google.com:443
Testing connection to the remote host with specific ssl version
openssl s_client -tls1_2 -connect google.com:443
Testing connection to the remote host with specific ssl cipher
openssl s_client -cipher 'AES128-SHA' -connect google.com:443
Generate private key without passphrase
# _len: 2048, 4096
( _fd="private.key" ; _len="4096" ; \
openssl genrsa -out ${_fd} ${_len} )
Generate private key with passphrase
# _ciph: des3, aes128, aes256
# _len: 2048, 4096
( _ciph="aes128" ; _fd="private.key" ; _len="4096" ; \
openssl genrsa -${_ciph} -out ${_fd} ${_len} )
Remove passphrase from private key
( _fd="private.key" ; _fd_unp="private_unp.key" ; \
openssl rsa -in ${_fd} -out ${_fd_unp} )
Encrypt existing private key with a passphrase
# _ciph: des3, aes128, aes256
( _ciph="aes128" ; _fd="private.key" ; _fd_pass="private_pass.key" ; \
openssl rsa -${_ciph} -in ${_fd} -out ${_fd_pass}
Check private key
( _fd="private.key" ; \
openssl rsa -check -in ${_fd} )
Get public key from private key
( _fd="private.key" ; _fd_pub="public.key" ; \
openssl rsa -pubout -in ${_fd} -out ${_fd_pub} )
Generate private key and CSR
( _fd="private.key" ; _fd_csr="request.csr" ; _len="4096" ; \
openssl req -out ${_fd_csr} -new -newkey rsa:${_len} -nodes -keyout ${_fd} )
Generate CSR
( _fd="private.key" ; _fd_csr="request.csr" ; \
openssl req -out ${_fd_csr} -new -key ${_fd} )
Generate CSR (metadata from existing certificate)
( _fd="private.key" ; _fd_csr="request.csr" ; _fd_crt="cert.crt" ; \
openssl x509 -x509toreq -in ${_fd_crt} -out ${_fd_csr} -signkey ${_fd} )
Generate CSR with -config param
( _fd="private.key" ; _fd_csr="request.csr" ; \
openssl req -new -sha256 -key ${_fd} -out ${_fd_csr} \
-config <(
cat <<-EOF
[req]
default_bits = 2048
prompt = no
default_md = sha256
req_extensions = req_ext
distinguished_name = dn

[ dn ]
C=<two-letter ISO abbreviation for your country>
ST=<state or province where your organization is legally located>
L=<city where your organization is legally located>
O=<legal name of your organization>
OU=<section of the organization>
CN=<fully qualified domain name>

[ req_ext ]
subjectAltName = @alt_names

[ alt_names ]
DNS.1 = <fully qualified domain name>
DNS.2 = <next domain>
DNS.3 = <next domain>
EOF
))
List available EC curves
openssl ecparam -list_curves
Generate ECDSA private key
# _curve: prime256v1, secp521r1, secp384r1
( _fd="private.key" ; _curve="prime256v1" ; \
openssl ecparam -out ${_fd} -name ${_curve} -genkey )

# _curve: X25519
( _fd="private.key" ; _curve="x25519" ; \
openssl genpkey -algorithm ${_curve} -out ${_fd} )
Print ECDSA private and public keys
( _fd="private.key" ; \
openssl ec -in ${_fd} -noout -text )

# For x25519 only extracting public key
( _fd="private.key" ; _fd_pub="public.key" ; \
openssl pkey -in ${_fd} -pubout -out ${_fd_pub} )
Generate private key with CSR (ECC)
# _curve: prime256v1, secp521r1, secp384r1
( _fd="domain.com.key" ; _fd_csr="domain.com.csr" ; _curve="prime256v1" ; \
openssl ecparam -out ${_fd} -name ${_curve} -genkey ; \
openssl req -new -key ${_fd} -out ${_fd_csr} -sha256 )
Generate self-signed certificate
# _len: 2048, 4096
( _fd="domain.key" ; _fd_out="domain.crt" ; _len="4096" ; _days="365" ; \
openssl req -newkey rsa:${_len} -nodes \
-keyout ${_fd} -x509 -days ${_days} -out ${_fd_out} )
Generate self-signed certificate from existing private key
# _len: 2048, 4096
( _fd="domain.key" ; _fd_out="domain.crt" ; _days="365" ; \
openssl req -key ${_fd} -nodes \
-x509 -days ${_days} -out ${_fd_out} )
Generate self-signed certificate from existing private key and csr
# _len: 2048, 4096
( _fd="domain.key" ; _fd_csr="domain.csr" ; _fd_out="domain.crt" ; _days="365" ; \
openssl x509 -signkey ${_fd} -nodes \
-in ${_fd_csr} -req -days ${_days} -out ${_fd_out} )
Generate DH Param key
openssl dhparam -out /etc/nginx/ssl/dhparam_4096.pem 4096
Convert DER to PEM
( _fd_der="cert.crt" ; _fd_pem="cert.pem" ; \
openssl x509 -in ${_fd_der} -inform der -outform pem -out ${_fd_pem} )
Convert PEM to DER
( _fd_der="cert.crt" ; _fd_pem="cert.pem" ; \
openssl x509 -in ${_fd_pem} -outform der -out ${_fd_der} )
Verification of the private key
( _fd="private.key" ; \
openssl rsa -noout -text -in ${_fd} )
Verification of the public key
# 1)
( _fd="public.key" ; \
openssl pkey -noout -text -pubin -in ${_fd} )

# 2)
( _fd="private.key" ; \
openssl rsa -inform PEM -noout -in ${_fd} &> /dev/null ; \
if [ $? = 0 ] ; then echo -en "OK\n" ; fi )
Verification of the certificate
( _fd="certificate.crt" ; # format: pem, cer, crt \
openssl x509 -noout -text -in ${_fd} )
Verification of the CSR
( _fd_csr="request.csr" ; \
openssl req -text -noout -in ${_fd_csr} )
Check whether the private key and the certificate match
(openssl rsa -noout -modulus -in private.key | openssl md5 ; \
openssl x509 -noout -modulus -in certificate.crt | openssl md5) | uniq
Tool: secure-delete
Secure delete with shred
shred -vfuz -n 10 file
shred --verbose --random-source=/dev/urandom -n 1 /dev/sda
Secure delete with scrub
scrub -p dod /dev/sda
scrub -p dod -r file
Secure delete with badblocks
badblocks -s -w -t random -v /dev/sda
badblocks -c 10240 -s -w -t random -v /dev/sda
Secure delete with secure-delete
srm -vz /tmp/file
sfill -vz /local
sdmem -v
swapoff /dev/sda5 && sswap -vz /dev/sda5
Tool: dd
Show dd status every so often
dd <dd_params> status=progress
watch --interval 5 killall -USR1 dd
Redirect output to a file with dd
echo "string" | dd of=filename
Tool: gpg
Export public key
gpg --export --armor "<username>" > username.pkey
--export - export all keys from all keyrings or specific key
-a|--armor - create ASCII armored output
Encrypt file
gpg -e -r "<username>" dump.sql
-e|--encrypt - encrypt data
-r|--recipient - encrypt for specific
Decrypt file
gpg -o dump.sql -d dump.sql.gpg
-o|--output - use as output file
-d|--decrypt - decrypt data (default)
Search recipient
gpg --keyserver hkp://keyserver.ubuntu.com --search-keys "<username>"
--keyserver - set specific key server
--search-keys - search for keys on a key server
Tool: system-other
Reboot system from init
exec /sbin/init 6
Init system from single user mode
exec /sbin/init
Show current working directory of a process
readlink -f /proc/<PID>/cwd
Show actual pathname of the executed command
readlink -f /proc/<PID>/exe
Tool: curl
curl -Iks https://www.google.com
-I - show response headers only
-k - insecure connection when using ssl
-s - silent mode (not display body)
curl -Iks --location -X GET -A "x-agent" https://www.google.com
--location - follow redirects
-X - set method
-A - set user-agent
curl -Iks --location -X GET -A "x-agent" --proxy http://127.0.0.1:16379 https://www.google.com
--proxy [socks5://|http://] - set proxy server
curl -o file.pdf -C - https://example.com/Aiju2goo0Ja2.pdf
-o - write output to file
-C - resume the transfer
Find your external IP address (external services)
curl ipinfo.io
curl ipinfo.io/ip
curl icanhazip.com
curl ifconfig.me/ip ; echo
Repeat URL request
# URL sequence substitution with a dummy query string:
curl -ks https://example.com/?[1-20]

# With shell 'for' loop:
for i in {1..20} ; do curl -ks https://example.com/ ; done
Check DNS and HTTP trace with headers for specific domains
### Set domains and external dns servers.
_domain_list=(google.com) ; _dns_list=("8.8.8.8" "1.1.1.1")

for _domain in "${_domain_list[@]}" ; do

printf '=%.0s' {1..48}

echo

printf "[\\e[1;32m+\\e[m] resolve: %s\\n" "$_domain"

for _dns in "${_dns_list[@]}" ; do

# Resolve domain.
host "${_domain}" "${_dns}"

echo

done

for _proto in http https ; do

printf "[\\e[1;32m+\\e[m] trace + headers: %s://%s\\n" "$_proto" "$_domain"

# Get trace and http headers.
curl -Iks -A "x-agent" --location "${_proto}://${_domain}"

echo

done

done

unset _domain_list _dns_list
Tool: httpie
http -p Hh https://www.google.com
-p - print request and response headers
H - request headers
B - request body
h - response headers
b - response body
http -p Hh https://www.google.com --follow --verify no
-F, --follow - follow redirects
--verify no - skip SSL verification
http -p Hh https://www.google.com --follow --verify no \
--proxy http:http://127.0.0.1:16379
--proxy [http:] - set proxy server
Tool: ssh
Escape Sequence
# Supported escape sequences:
~. - terminate connection (and any multiplexed sessions)
~B - send a BREAK to the remote system
~C - open a command line
~R - Request rekey (SSH protocol 2 only)
~^Z - suspend ssh
~# - list forwarded connections
~& - background ssh (when waiting for connections to terminate)
~? - this message
~~ - send the escape character by typing it twice
Compare a remote file with a local file
ssh user@host cat /path/to/remotefile | diff /path/to/localfile -
SSH connection through host in the middle
ssh -t reachable_host ssh unreachable_host
Run command over SSH on remote host
cat > cmd.txt << __EOF__
cat /etc/hosts
__EOF__

ssh host -l user $(<cmd.txt)
Get public key from private key
ssh-keygen -y -f ~/.ssh/id_rsa
Get all fingerprints
ssh-keygen -l -f .ssh/known_hosts
SSH authentication with user password
ssh -o PreferredAuthentications=password -o PubkeyAuthentication=no user@remote_host
SSH authentication with publickey
ssh -o PreferredAuthentications=publickey -o PubkeyAuthentication=yes -i id_rsa user@remote_host
Simple recording SSH session
function _ssh_sesslog() {

_sesdir="<path/to/session/logs>"

mkdir -p "${_sesdir}" && \
ssh $@ 2>&1 | tee -a "${_sesdir}/$(date +%Y%m%d).log"

}

# Alias:
alias ssh='_ssh_sesslog'
Using Keychain for SSH logins
### Delete all of ssh-agent's keys.
function _scl() {

/usr/bin/keychain --clear

}

### Add key to keychain.
function _scg() {

/usr/bin/keychain /path/to/private-key
source "$HOME/.keychain/$HOSTNAME-sh"

}
SSH login without processing any login scripts
ssh -tt user@host bash
SSH local port forwarding
Example 1:

# Forwarding our local 2250 port to nmap.org:443 from localhost through localhost
host1> ssh -L 2250:nmap.org:443 localhost

# Connect to the service:
host1> curl -Iks --location -X GET https://localhost:2250
Example 2:

# Forwarding our local 9051 port to db.d.x:5432 from localhost through node.d.y
host1> ssh -nNT -L 9051:db.d.x:5432 node.d.y

# Connect to the service:
host1> psql -U db_user -d db_dev -p 9051 -h localhost
-n - redirects stdin from /dev/null
-N - do not execute a remote command
-T - disable pseudo-terminal allocation
SSH remote port forwarding
# Forwarding our local 9051 port to db.d.x:5432 from host2 through node.d.y
host1> ssh -nNT -R 9051:db.d.x:5432 node.d.y

# Connect to the service:
host2> psql -U postgres -d postgres -p 8000 -h localhost
Tool: linux-dev
Testing remote connection to port
timeout 1 bash -c "</dev/<proto>/<host>/<port>" >/dev/null 2>&1 ; echo $?
<proto - set protocol (tcp/udp)
<host> - set remote host
<port> - set destination port
Read and write to TCP or UDP sockets with common bash tools
exec 5<>/dev/tcp/<host>/<port>; cat <&5 & cat >&5; exec 5>&-
Tool: tcpdump
Filter incoming (on interface) traffic (specific ip:port)
tcpdump -ne -i eth0 -Q in host 192.168.252.1 and port 443
-n - don't convert addresses (-nn will not resolve hostnames or ports)
-e - print the link-level headers
-i [iface|any] - set interface
-Q|-D [in|out|inout] - choose send/receive direction (-D - for old tcpdump versions)
host [ip|hostname] - set host, also [host not]
[and|or] - set logic
port [1-65535] - set port number, also [port not]
Filter incoming (on interface) traffic (specific ip:port) and write to a file
tcpdump -ne -i eth0 -Q in host 192.168.252.1 and port 443 -c 5 -w tcpdump.pcap
-c [num] - capture only num number of packets
-w [filename] - write packets to file, -r [filename] - reading from file
Capture all ICMP packets
tcpdump -nei eth0 icmp
Check protocol used (TCP or UDP) for service
tcpdump -nei eth0 tcp port 22 -vv -X | egrep "TCP|UDP"
Display ASCII text (to parse the output using grep or other)
tcpdump -i eth0 -A -s0 port 443
Grab everything between two keywords
tcpdump -i eth0 port 80 -X | sed -n -e '/username/,/=ldap/ p'
Grab user and pass ever plain http
tcpdump -i eth0 port http -l -A | egrep -i \
'pass=|pwd=|log=|login=|user=|username=|pw=|passw=|passwd=|password=|pass:|user:|username:|password:|login:|pass |user ' \
--color=auto --line-buffered -B20
Extract HTTP User Agent from HTTP request header
tcpdump -ei eth0 -nn -A -s1500 -l | grep "User-Agent:"
Capture only HTTP GET and POST packets
tcpdump -ei eth0 -s 0 -A -vv \
'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420' or 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354'
or simply:

tcpdump -ei eth0 -s 0 -v -n -l | egrep -i "POST /|GET /|Host:"
Rotate capture files
tcpdump -ei eth0 -w /tmp/capture-%H.pcap -G 3600 -C 200
-G <num> - pcap will be created every <num> seconds
-C <size> - close the current pcap and open a new one if is larger than <size>
Top hosts by packets
tcpdump -ei enp0s25 -nnn -t -c 200 | cut -f 1,2,3,4 -d '.' | sort | uniq -c | sort -nr | head -n 20
Excludes any RFC 1918 private address
tcpdump -nei eth0 'not (src net (10 or 172.16/12 or 192.168/16) and dst net (10 or 172.16/12 or 192.168/16))'
Tool: tcpick
Analyse packets in real-time
while true ; do tcpick -a -C -r dump.pcap ; sleep 2 ; clear ; done
Tool: ngrep
ngrep -d eth0 "www.domain.com" port 443
-d [iface|any] - set interface
[domain] - set hostname
port [1-65535] - set port number
ngrep -d eth0 "www.domain.com" src host 10.240.20.2 and port 443
(host [ip|hostname]) - filter by ip or hostname
(port [1-65535]) - filter by port number
ngrep -d eth0 -qt -O ngrep.pcap "www.domain.com" port 443
-q - quiet mode (only payloads)
-t - added timestamps
-O [filename] - save output to file, -I [filename] - reading from file
ngrep -d eth0 -qt 'HTTP' 'tcp'
HTTP - show http headers
tcp|udp - set protocol
[src|dst] host [ip|hostname] - set direction for specific node
ngrep -l -q -d eth0 -i "User-Agent: curl*"
-l - stdout line buffered
-i - case-insensitive search
Tool: hping3
hping3 -V -p 80 -s 5050 <scan_type> www.google.com
-V|--verbose - verbose mode
-p|--destport - set destination port
-s|--baseport - set source port
<scan_type> - set scan type
-F|--fin - set FIN flag, port open if no reply
-S|--syn - set SYN flag
-P|--push - set PUSH flag
-A|--ack - set ACK flag (use when ping is blocked, RST response back if the port is open)
-U|--urg - set URG flag
-Y|--ymas - set Y unused flag (0x80 - nullscan), port open if no reply
-M 0 -UPF - set TCP sequence number and scan type (URG+PUSH+FIN), port open if no reply
hping3 -V -c 1 -1 -C 8 www.google.com
-c [num] - packet count
-1 - set ICMP mode
-C|--icmptype [icmp-num] - set icmp type (default icmp-echo = 8)
hping3 -V -c 1000000 -d 120 -S -w 64 -p 80 --flood --rand-source <remote_host>
--flood - sent packets as fast as possible (don't show replies)
--rand-source - random source address mode
-d --data - data size
-w|--win - winsize (default 64)
Tool: nmap
Ping scans the network
nmap -sP 192.168.0.0/24
Show only open ports
nmap -F --open 192.168.0.0/24
Full TCP port scan using with service version detection
nmap -p 1-65535 -sV -sS -T4 192.168.0.0/24
Nmap scan and pass output to Nikto
nmap -p80,443 192.168.0.0/24 -oG - | nikto.pl -h -
Recon specific ip:service with Nmap NSE scripts stack
# Set variables:
_hosts="192.168.250.10"
_ports="80,443"

# Set Nmap NSE scripts stack:
_nmap_nse_scripts="+dns-brute,\
+http-auth-finder,\
+http-chrono,\
+http-cookie-flags,\
+http-cors,\
+http-cross-domain-policy,\
+http-csrf,\
+http-dombased-xss,\
+http-enum,\
+http-errors,\
+http-git,\
+http-grep,\
+http-internal-ip-disclosure,\
+http-jsonp-detection,\
+http-malware-host,\
+http-methods,\
+http-passwd,\
+http-phpself-xss,\
+http-php-version,\
+http-robots.txt,\
+http-sitemap-generator,\
+http-shellshock,\
+http-stored-xss,\
+http-title,\
+http-unsafe-output-escaping,\
+http-useragent-tester,\
+http-vhosts,\
+http-waf-detect,\
+http-waf-fingerprint,\
+http-xssed,\
+traceroute-geolocation.nse,\
+ssl-enum-ciphers,\
+whois-domain,\
+whois-ip"

# Set Nmap NSE script params:
_nmap_nse_scripts_args="dns-brute.domain=${_hosts},http-cross-domain-policy.domain-lookup=true,"
_nmap_nse_scripts_args+="http-waf-detect.aggro,http-waf-detect.detectBodyChanges,"
_nmap_nse_scripts_args+="http-waf-fingerprint.intensive=1"

# Perform scan:
nmap --script="$_nmap_nse_scripts" --script-args="$_nmap_nse_scripts_args" -p "$_ports" "$_hosts"
Tool: netcat
nc -kl 5000
-l - listen for an incoming connection
-k - listening after client has disconnected
>filename.out - save receive data to file (optional)
nc 192.168.0.1 5051 < filename.in
< filename.in - send data to remote host
nc -vz 10.240.30.3 5000
-v - verbose output
-z - scan for listening daemons
nc -vzu 10.240.30.3 1-65535
-u - scan only udp ports
Transfer data file (archive)
server> nc -l 5000 | tar xzvfp -
client> tar czvfp - /path/to/dir | nc 10.240.30.3 5000
Launch remote shell
server> nc -l 5000 -e /bin/bash
client> nc 10.240.30.3 5000
Simple file server
while true ; do nc -l 5000 | tar -xvf - ; done
Simple minimal HTTP Server
while true ; do nc -l -p 1500 -c 'echo -e "HTTP/1.1 200 OK\n\n $(date)"' ; done
Simple HTTP Server
Restarts web server after each request - remove while condition for only single connection.

cat > index.html << __EOF__
<!doctype html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title></title>
<meta name="description" content="">
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>

<p>

Hello! It's a site.

</p>

</body>
</html>
__EOF__
server> while : ; do \
(echo -ne "HTTP/1.1 200 OK\r\nContent-Length: $(wc -c <index.html)\r\n\r\n" ; cat index.html;) | \
nc -l -p 5000 \
; done
-p - port number
Simple HTTP Proxy (single connection)
#!/usr/bin/env bash

if [[ $# != 2 ]] ; then
printf "%s\\n" \
"usage: ./nc-proxy listen-port bk_host:bk_port"
fi

_listen_port="$1"
_bk_host=$(echo "$2" | cut -d ":" -f1)
_bk_port=$(echo "$2" | cut -d ":" -f2)

printf " lport: %s\\nbk_host: %s\\nbk_port: %s\\n\\n" \
"$_listen_port" "$_bk_host" "$_bk_port"

_tmp=$(mktemp -d)
_back="$_tmp/pipe.back"
_sent="$_tmp/pipe.sent"
_recv="$_tmp/pipe.recv"

trap 'rm -rf "$_tmp"' EXIT

mkfifo -m 0600 "$_back" "$_sent" "$_recv"

sed "s/^/=> /" <"$_sent" &
sed "s/^/<= /" <"$_recv" &

nc -l -p "$_listen_port" <"$_back" | \
tee "$_sent" | \
nc "$_bk_host" "$_bk_port" | \
tee "$_recv" >"$_back"
server> chmod +x nc-proxy && ./nc-proxy 8080 192.168.252.10:8000
lport: 8080
bk_host: 192.168.252.10
bk_port: 8000

client> http -p h 10.240.30.3:8080
HTTP/1.1 200 OK
Accept-Ranges: bytes
Cache-Control: max-age=31536000
Content-Length: 2748
Content-Type: text/html; charset=utf-8
Date: Sun, 01 Jul 2018 20:12:08 GMT
Last-Modified: Sun, 01 Apr 2018 21:53:37 GMT
Create a single-use TCP or UDP proxy
### TCP -> TCP
nc -l -p 2000 -c "nc [ip|hostname] 3000"

### TCP -> UDP
nc -l -p 2000 -c "nc -u [ip|hostname] 3000"

### UDP -> UDP
nc -l -u -p 2000 -c "nc -u [ip|hostname] 3000"

### UDP -> TCP
nc -l -u -p 2000 -c "nc [ip|hostname] 3000"
Tool: gnutls-cli
Testing connection to remote host (with SNI support)
gnutls-cli -p 443 google.com
Testing connection to remote host (without SNI support)
gnutls-cli --disable-sni -p 443 google.com
Tool: socat
Testing remote connection to port
socat - TCP4:10.240.30.3:22
- - standard input (STDIO)
TCP4:<params> - set tcp4 connection with specific params
[hostname|ip] - set hostname/ip
[1-65535] - set port number
Redirecting TCP-traffic to a UNIX domain socket under Linux
socat TCP-LISTEN:1234,bind=127.0.0.1,reuseaddr,fork,su=nobody,range=127.0.0.0/8 UNIX-CLIENT:/tmp/foo
TCP-LISTEN:<params> - set tcp listen with specific params
[1-65535] - set port number
bind=[hostname|ip] - set bind hostname/ip
reuseaddr - allows other sockets to bind to an address
fork - keeps the parent process attempting to produce more connections
su=nobody - set user
range=[ip-range] - ip range
UNIX-CLIENT:<params> - communicates with the specified peer socket
filename - define socket
Tool: p0f
Set iface in promiscuous mode and dump traffic to the log file
p0f -i enp0s25 -p -d -o /dump/enp0s25.log
-i - listen on the specified interface
-p - set interface in promiscuous mode
-d - fork into background
-o - output file
Tool: netstat
Graph # of connections for each hosts
netstat -an | awk '/ESTABLISHED/ { split($5,ip,":"); if (ip[1] !~ /^$/) print ip[1] }' | \
sort | uniq -c | awk '{ printf("%s\t%s\t",$2,$1) ; for (i = 0; i < $1; i++) {printf("*")}; print "" }'
Monitor open connections for specific port including listen, count and sort it per IP
watch "netstat -plan | grep :443 | awk {'print \$5'} | cut -d: -f 1 | sort | uniq -c | sort -nk 1"
Grab banners from local IPv4 listening ports
netstat -nlt | grep 'tcp ' | grep -Eo "[1-9][0-9]*" | xargs -I {} sh -c "echo "" | nc -v -n -w1 127.0.0.1 {}"
Tool: rsync
Rsync remote data as root using sudo
rsync --rsync-path 'sudo rsync' username@hostname:/path/to/dir/ /local/
Tool: host
Resolves the domain name (using external dns server)
host google.com 9.9.9.9
Checks the domain administrator (SOA record)
host -t soa google.com 9.9.9.9
Tool: dig
Resolves the domain name (short output)
dig google.com +short
Lookup NS record for specific domain
dig @9.9.9.9 google.com NS
Query only answer section
dig google.com +nocomments +noquestion +noauthority +noadditional +nostats
Query ALL DNS Records
dig google.com ANY +noall +answer
DNS Reverse Look-up
dig -x 172.217.16.14 +short
Tool: certbot
Generate multidomain certificate
certbot certonly -d example.com -d www.example.com
Generate wildcard certificate
certbot certonly --manual --preferred-challenges=dns -d example.com -d *.example.com
Generate certificate with 4096 bit private key
certbot certonly -d example.com -d www.example.com --rsa-key-size 4096
Tool: network-other
Get all subnets for specific AS (Autonomous system)
AS="AS32934"
whois -h whois.radb.net -- "-i origin ${AS}" | \
grep "^route:" | \
cut -d ":" -f2 | \
sed -e 's/^[ \t]//' | \
sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 | \
cut -d ":" -f2 | \
sed -e 's/^[ \t]/allow /' | \
sed 's/$/;/' | \
sed 's/allow */subnet -> /g'
Resolves domain name from dns.google.com with curl and jq
_dname="google.com" ; curl -s "https://dns.google.com/resolve?name=${_dname}&type=A" | jq .
Tool: git
Log alias for a decent view of your repo
# 1)
git log --oneline --decorate --graph --all

# 2)
git log --graph \
--pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' \
--abbrev-commit
Tool: python
Static HTTP web server
# Python 3.x
python3 -m http.server 8000 --bind 127.0.0.1

# Python 2.x
python -m SimpleHTTPServer 8000
Static HTTP web server with SSL support
# Python 3.x
from http.server import HTTPServer, BaseHTTPRequestHandler
import ssl

httpd = HTTPServer(('localhost', 4443), BaseHTTPRequestHandler)

httpd.socket = ssl.wrap_socket (httpd.socket,
keyfile="path/to/key.pem",
certfile='path/to/cert.pem', server_side=True)

httpd.serve_forever()

# Python 2.x
import BaseHTTPServer, SimpleHTTPServer
import ssl

httpd = BaseHTTPServer.HTTPServer(('localhost', 4443),
SimpleHTTPServer.SimpleHTTPRequestHandler)

httpd.socket = ssl.wrap_socket (httpd.socket,
keyfile="path/tp/key.pem",
certfile='path/to/cert.pem', server_side=True)

httpd.serve_forever()
Encode base64
python -m base64 -e <<< "sample string"
Decode base64
python -m base64 -d <<< "dGhpcyBpcyBlbmNvZGVkCg=="
Tool: awk
Remove duplicate entries in a file without sorting
awk '!x[$0]++' filename
Print the last column
awk '{print $NF}' filename
Remove empty lines
awk 'NF > 0' filename

# alternative:
awk NF filename
Print multiple columns with separators
awk -F' ' '{print "ip:\t" $2 "\n port:\t" $3' filename
Exclude multiple columns
awk '{$1=$3=""}1' filename
Get the last hour of Apache logs
awk '/'$(date -d "1 hours ago" "+%d\\/%b\\/%Y:%H:%M")'/,/'$(date "+%d\\/%b\\/%Y:%H:%M")'/ { print $0 }' \
/var/log/httpd/access_log
Tool: sed
To print a specific line from a file
sed -n 10p /path/to/file
Remove a specific line from a file
sed -i 10d /path/to/file
# alternative (BSD): sed -i'' 10d /path/to/file
Remove a range of lines from a file
sed -i <file> -re '<start>,<end>d'
Replace newline(s) with a space
sed ':a;N;$!ba;s/\n/ /g' /path/to/file

# cross-platform compatible syntax:
sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ /g' /path/to/file
:a create a label a
N append the next line to the pattern space
$! if not the last line, ba branch (go to) label a
s substitute, /\n/ regex for new line, / / by a space, /g global match (as many times as it can)
Alternatives:

# perl version (sed-like speed):
perl -p -e 's/\n/ /' /path/to/file

# bash version (slow):
while read line ; do printf "%s" "$line " ; done < file
Delete string +N next lines
sed '/start/,+4d' /path/to/file
Tool: grep
Search for a "pattern" inside all files in the current directory
grep -rn "pattern"
grep -RnisI "pattern" *
fgrep "pattern" * -R
Remove blank lines from a file and save output to new file
grep . filename > newfilename
Show only for multiple patterns
grep 'INFO*'\''WARN' filename
grep 'INFO\|WARN' filename
grep -e INFO -e WARN filename
grep -E '(INFO|WARN)' filename
egrep "INFO|WARN" filename
Except multiple patterns
grep -vE '(error|critical|warning)' filename
Show data from file without comments
grep -v ^[[:space:]]*# filename
Show data from file without comments and new lines
egrep -v '#|^$' filename
Show strings with a dash/hyphen
grep -e -- filename
grep -- -- filename
grep "\-\-" filename
Shell functions [TOC]
Table of Contents
Domain resolve
Get ASN
Domain resolve
# Dependencies:
# - curl
# - jq

function DomainResolve() {

local _host="$1"

local _curl_base="curl --request GET"
local _timeout="15"

_host_ip=$($_curl_base -ks -m "$_timeout" "https://dns.google.com/resolve?name=${_host}&type=A" | \
jq '.Answer[0].data' | tr -d "\"" 2>/dev/null)

if [[ -z "$_host_ip" ]] || [[ "$_host_ip" == "null" ]] ; then

echo -en "Unsuccessful domain name resolution.\\n"

else

echo -en "$_host > $_host_ip\\n"

fi

}
Example:

shell> DomainResolve nmap.org
nmap.org > 45.33.49.119

shell> DomainResolve nmap.org
Unsuccessful domain name resolution.
Get ASN
# Dependencies:
# - curl
# - python

function GetASN() {

local _ip="$1"

local _curl_base="curl --request GET"
local _timeout="15"

_asn=$($_curl_base -ks -m "$_timeout" "http://ip-api.com/json/${_ip}" | \
python -c 'import sys, json; print json.load(sys.stdin)["as"]' 2>/dev/null)

_state=$(echo $?)

if [[ -z "$_ip" ]] || [[ "$_ip" == "null" ]] || [[ "$_state" -ne 0 ]]; then

echo -en "Unsuccessful ASN gathering.\\n"

else

echo -en "$_ip > $_asn\\n"

fi

}
Example:

shell> GetASN 1.1.1.1
1.1.1.1 > AS13335 Cloudflare, Inc.

shell> GetASN 0.0.0.0
Unsuccessful ASN gathering.