# find largest 15 directories or files find . -type d -print0 | xargs -0 du -s | sort -n | tail -15 | cut -f2 | xargs -I{} du -sh {} find . -type f -print0 | xargs -0 du -s | sort -n | tail -15 | cut -f2 | xargs -I{} du -sh {}
scp localfile user@remotecomputer:/path/to/target/dir diff file1 file2 dd if=/dev/cdrom | bzip2 | ssh user@domain.com 'bunzip2 | cat > file.iso' useradd -M -G group user ssh host 'cat >> .ssh/authorized_keys2' < .ssh/id_rsa.pub
File System Managment
fdisk /dev/sda df -h resize2fs /dev/sdb2 mke2fs /dev/sda1 mkfs.ext3 /dev/sda1 mkfs.ext4 /dev/sda1 //Upgrading from ext3 to ext4 umount /dev/sda2 tune2fs -O extents,uninit_bg,dir_index /dev/sda2 e2fsck -pf /dev/sda2 mount /dev/sda2 /home
Compressing Tars
tar cf dir.tar dir/ tar czf dir.tar.gz dir/ tar cjf dir.tar.bz2 dir/
Decompressing Tars
tar xf dir.tar tar xzf dir.tar.gz tar xjf dir.tar.bz2
Resume and scp transfer
rsync --partial --progress --rsh=ssh host:remote_file local_file rsync -P -e ssh host:<remote file> <local file>
Find ports without detection that are open
nmap -FsS domain.com
SED
sed -i -e 's/-/t-/' file.txt"
Update iptables firewall
/etc/init.d/fail2ban stop iptables-restore < /system/configuration/firewall.txt /etc/init.d/iptables save /etc/init.d/fail2ban start
Count fail2ban ip blocks
iptables -nvL | grep -A 100000 'Chain fail2ban-SSH' | wc -l
Remove ip address from iptables fail2ban list
iptables -nL | grep -A 100000 'Chain fail2ban-SSH' iptables -D fail2ban-SSH <line number>
Common everyday should know
ls cd mv rm cp man ssh awk sed mysql -u root -p grep head tail watch whois dig host curl htop kill echo cat zip g++ javac vim clear