Here I collect some commands that I often need but always forget.

Reconstruct standard permissions for directories and files in current directory

for i in `find .`; do [ -d $i ] && chmod 755 $i || chmod 644 $i; done

Find the command line of a program using a specific port

port=22
pid=$(lsof -Pan -i tcp -i udp | grep ":$port"|tr -s " " | cut -d" " -f2)
ps -Afe|grep "$pid"|grep --invert-match grep | sed "s/^\\([^ ]*[ ]*\\)\\{7\\}\\(.*\\)$/\\2/g"

Get the header of a website

curl -sI $URL

Get your current public IP address

curl ip.binfalse.de

Discover running Hosts in a Network

nmap -sP 192.168.1.*

Find large files recursively

find . -type f -size +50M -exec du -h {} \; | sort -n

Find files that have been modified in the past 60 minutes

find . -mmin 60 -type f

Convert encoding of a file

iconv -f utf8 -t utf16 /path/to/file

Unmount all NFS-mounts

umount -a -t nfs

Speed up copying

( cd /olddir ; tar cf - * ) | ( cd /newdir ; tar xvf - )

Merge various PDF files

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=output.pdf -dBATCH first.pdf second.pdf

Convert spaces in file names to underscores

rename 'y/ /_/' *

Boot another OS at next startup

echo "savedefault --default=2 --once" | grub --batch; sudo reboot

Convert .flv to .avi

mencoder input.flv -ovc lavc -oac mp3lame -o output.avi

Delete all Flash cookies

find $HOME -name '*.sol' -exec rm {} \\;

Delete all crappy adobe/flash stuff:

rm -rf $HOME/.adobe $HOME/.macromedia

Display some cert infos

openssl s_client -connect google.de:443 2>/dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' | openssl x509 -noout -subject -issuer -dates -hash -fingerprint

Of course also applicable for other ports than HTTPS .

List connected LDAP clients

# Linux
netstat -n inet | awk '/:636/{print $5}' | cut -f1 -d: | sort -u
# Solaris
netstat -n -f inet | awk '/\\.636/{print $2}' | cut -f1-4 -d. | sort -u

If you aren’t using encrypted connections replace 636 with 389 .