Useful Linux/Unix commands

• How do I find all files containing specific text?

grep -rnw '/path/to/somewhere/' -e 'pattern'

• How i change the default file permissions (mask that controls file permissions)

umask

• Untar (unzip) file

tar -zxvf archive.tar.gz

• Copy files via rsync from one host to another

rsync -av [USER@]HOST[:PORT]/SOURCE [USER@]HOST[:PORT]/DEST

• nslookup missing? Install dig

sudo apt-get install dnsutils

• find without “Permission denied”

find / -name 'filename.ext' 2>&1 | grep -v "Permission denied"

• flush dns cache

sudo systemd-resolve --flush-caches

• show open ports

netstat -tulpn

• Directory size

du -sh /var
du -shc /var/*
du -h --max-depth=1 /var
du -sh /var/lib/docker/containers/*/*.log

• Search multiple PDF files for a “needle”

pdfgrep -i needle haystack*.pdf

• Show hidden files with ls

ls -lar