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Basic

Find a file

find / -name *REPLACE_NAME_PART* -type f

Script to add to .bash_profile to load .bashrc

if [ -f ~/.bashrc ]; then
	. ~/.bashrc
fi

Clean output when running a command that may throw errors

REPLACE_COMMAND 2> /dev/null

Don’t get either output or errors

It will send errors to standard output, and output to null:

REPLACE_COMMAND > /dev/null 2>&1

Another way, redirecting both output and error to null:

REPLACE_COMMAND &> /dev/null

List files ordered by last modification time

ls -ltr

Create a folder and sub-folders and not fail if it already exists

mkdir -p REPLACE/FOLDER/PATH

Automate actions to do on folders or sub-folders with Bash

for folder in *;do echo ${folder};cd ${folder};ADD_OTHER_ACTIONS;cd ../;done;

Get the logs from a specific date

Useful if we don’t have access to them in Kibana

ls -l --time-style="+%Y-%m-%d" libs | grep '2022-08'

Run a command on a host

ssh REPLACE_HOST 'REPLACE_COMMAND_TO_RUN'

Find a command used recently

history | grep REPLACE_COMMAND_TO_SEARCH

Start, stop or restart services, or get their status

/usr/bin/systemctl REPLACE_OPERATION REPLACE_SERVICE_NAME

Delete files except the most recent ones

find ${REPLACE_FILE_PATTERN} -mtime +${REPLACE_DATES_TO_KEEP} -delete"

Copy files from one host to another

rsync -avh SOURCE_PATH DESTINATION_PATH

Generate a random password

openssl rand -base64 32

Decode text in base64

echo REPLACE_TEXT | base64 --decode

Encode text in base64

echo -n REPLACE_TEXT | base64

Create aliases receiving input params

We can use functions for them. We can add them to a script that is loaded from .bashrc using

". REPLACE_SCRIPT_PATH"

REPLACE_FUNCTION_NAME () {
   # Do any desired action using $1... for the input params
}

Main folders in Unix

A great diagram a colleague shared with me a while back. I hope I will find who created it to say thanks and give them the credit they deserve for it

User and group management

Group limitation

Unix systems (using NFS) only allow membership to 16 groups. Users with access to more than that may experience problems accessing files for some groups

Find the groups the current user has access to

id -a
groups

Networking

Find the service running on a port:

Multiple ways:

• lsof -i :REPLACE_PORT
• fuser REPLACE_PORT/tcp
• ps -ef | grep REPLACE_PORT
• netstat -nat | grep LISTEN | grep REPLACE_PORT

Open a port on a Unix box server to check connectivity from outside

nc -kv4 -l REPLACE_PORT > REPLACE_LOG_FILE_PATH 2>&1 &

The last part is to get logs from both normal and error outputs

Connect from local to a website using SSH tunneling

When the box where it runs is not directly accessible and we have to access it through another server:

ssh -L LOCAL_PORT:HOST:REMOTE_PORT -N -f USER_ID@HOST

On the web browser open localhost referencing that port, for example:

https://localhost:LOCAL_PORT

Test the download speed of the internet connection

Download a big file and see its file and the download time. Not accurate but gives an idea.

wget -O /dev/null REPLACE_BIG_FILE_LINK

Prevent SSL_ERROR_SYSCALL when doing connectivity tests

export NO_PROXY=BASE_DNS_DESTINATION_ENDPOINT

Test connectivity without proxy

Different ways:

• curl REPLACE_DESTINATION_HOST REPLACE_DESTINATION_PORT
• telnet REPLACE_DESTINATION_HOST REPLACE_DESTINATION_PORT
• nc -vz REPLACE_DESTINATION_IP_ADDRESS REPLACE_DESTINATION_PORT

Test connectivity via proxy with telnet

Connect to the proxy via telnet:

telnet REPLACE_PROXY_DNS REPLACE_PROXY_PORT

And once connected run this to check the proxy can connect to the destination:

CONNECT REPLACE_DESTINATION_HOST:REPLACE_DESTINATION_PORT

Test connectivity via proxy without telnet

export http_proxy=REPLACE_PROXY_DNS:REPLACE_PROXY_PORT
export https_proxy=REPLACE_PROXY_DNS:REPLACE_PROXY_PORT
curl REPLACE_DESTINATION_HOST:REPLACE_DESTINATION_PORT

Disk and memory checks

Check disk space

See the space available on the main folders:

df -kh

See the space used by the folders under the current folder:

du -skh *

See space available in a location

df -H REPLACE_LOCATION_PATH

See where a volume is mounted

df -kh .

See processes using most memory

• ps aux –sort=-%mem | head
• ps -o pid,user,%mem,command ax | sort -b -k3 -r

See the network interfaces configured in a host

ip link show

See the network interfaces in which a port is running

netstat -tnl | grep REPLACE_PORT

See the routes configured in a host

route -n

File compression

Compress files with password

zip -e files.zip files_to_add

Uncompress 7z files

7za x myfiles.7z

Uncompress tar files

tar -zxvf REPLACE_TAR_FILE_NAME -C REPLACE_DESTINATION_PATH

Compress files with tar

Always use local relative path instead of absolute ones with tar. Tar puts the files together, gzip compresses then:

1. tar -cvzf REPLACE_TAR_FILE_NAME REPLACE_FOLDER_TO_COMPRESS
2. gzip REPLACE_TAR_FILE_PATH

Uncompress gzip files

gzip -d REPLACE_FILE_PATH

Cron schedulers

They all require systemd or systemctl:

• cron
• cronie
• anacron

Other schedulers

• watch: it doesn’t seem to work inside a script
• Use an external scheduler such as Control-m
• Use a “while true” combined with sleep in Bash script if the other options are not available