linux-useful-commands

Just another reference to linux useful commands

General

cat with grep and surrounding lines

cat file.logs | grep "Desired word to be located" -C 50
# - -A (after)
# - -B (before)
# - -C (context [before + after])

Windows to Unix - Convert all files recursively

find . -type f -print0 | xargs -0 dos2unix

Clear and Edit File

cat /dev/null > file.sh && vi file.sh

Retrieve jobs running in background

#  If you have more than one process running in the background, do this:
jobs

# use the fg to get the job by the index 
fg %3

Locate File

sudo find . -type f -name "*.crt"
sudo find . -type f -name "FileName"

SO UPDATES

Change the overcommit strategy

sysctl -a | grep overco
sysctl -w vm.overcommit_memory=1
sysctl -w vm.swappiness=1

Increase Open File Limit

* - nofile 16384

/etc/security/limit.conf
# Edit the /etc/security/limit.conf file.
# Change the statement that specifies the value of nofiles to 8000.
# If you want the change to take effect in the current session, type ulimit -n 8000.

JSON on Bash - Get value on a base array

yum install jq
cat example.json | jq '.[] | .HostsPath'

---

Server Resources Check

PS order by Memory

ps aux  | awk '{print $6/1024 " MB\t\t" $11}'  | sort -n
ps aux  | sort -n
ps aux --sort -rss
ps aux | sort -rn -k 5,6
ps --sort -rss -eo rss,pid,command | head
ps aux | awk '{print $4"\t"$11}' | sort | uniq -c | awk '{print $2" "$1" "$3}' | sort -nr

Process Tree

pstree -hgcp

Hard Disk usage

df -h

Available RAM Memory

free -m

cpu, ram stats

vmstat -SM 1 100

shell alias  

alias ducks='du -cks * | sort -rn | head'
ducks

Test websocket with Curl

curl --include \
     --no-buffer \
     --header "Connection: Upgrade" \
     --header "Upgrade: websocket" \
     --header "Host: localhost:80" \
     --header "Origin: http://localhost:80" \
     --header "Sec-WebSocket-Key: SGVsbG8sIHdvcmxkIQ==" \
     --header "Sec-WebSocket-Version: 13" \
     http://localhost:80/

Copy ssh keys

ssh-copy-id -i ~/.ssh/mykey user@host

restart network interfaces

sudo ip addr flush interface-name
sudo systemctl restart networking

Check open ports without netstat or lsof

declare -a array=($(tail -n +2 /proc/net/tcp | cut -d":" -f"3"|cut -d" " -f"1")) && for port in ${array[@]}; do echo $((0x$port)); done

Sharing Folder 

mount -t cifs -o username=<change it> //network-folder /local-folder

Check Firewalld Status 

systemctl status firewalld.service
sudo firewall-cmd --permanent --zone=trusted --add-interface=docker0
sudo firewall-cmd --reload

Check Iptables Status

sudo iptables -L
sudo iptables -L --line-numbers
sudo iptables -A FORWARD -i docker0 -o eth0 -j ACCEPT
sudo iptables -A FORWARD -i eth0 -o docker0 -j ACCEPT
sudo iptables -I INPUT -j ACCEPT

sudo journalctl -fu NetworkManager

TCP Null Scan to fool a firewall to generate a response

## Does not set any bits (TCP flag header is 0) ##
nmap -sN 192.168.0.1

TCP Fin scan to check firewall

## Sets just the TCP FIN bit ##
nmap -sF 192.168.0.1

TCP Xmas scan to check firewall

## Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree ##
nmap -sX 192.168.0.1

Complete check

nmap -v -sS -A -T4 192.168.0.1

Realtime Packages Received

watch -n1 -d "iptables -vnxL | grep -v -e pkts -e Chain | sort -nk1 | tac | column -t"