==== 20 Comandos Úteis ====


1. Drag about how much free RAM you have on Linux: 
<code>free</code>


2. Where is that application I just installed (all directories) 
<code>whereis [app]</code>


3. Disk space usage 
<code>df -h</code>


4. To make a playlist of the audio files in a folder 
<code>ls -R > playlist.m3u</code>


5. To kill a process by it's name: 
<code>sudo killall <prog_name></code> 

for instance: sudo killall firefox. Or you can kill by pid (program id): 
<code>sudo kill <pid></code>

and to see the pid: 
<code>pidof <program name></code>

for instance: pidof firefox or you can try listing the currently running processes with: 
<code>ps -e</code>


6. To find out the version of installed software: 
<code>apt-cache policy <packet_name></code>


7. To find out the UUID of your partitions: 
<code>ls /dev/disk/by-uuid/ -alh
</code>


8. Display the top ten running processes - sorted by memory usage: 
<code>ps aux | sort -nrk 4 | head</code>


9. Set audible alarm when an IP address comes online 
<code>ping -i 60 -a IP_address</code>


10. Mount a .iso file in UNIX/Linux: 
<code>mount /path/to/file.iso /mnt/cdrom -oloop</code>


11. Sharing a file through http 80 port: 
<code>nc -w 5 -v -l -p 80 < file.ext</code>

From the other machine open a web navigator and go to ip from the machine who launch netcat, "http://ip-address/"
If you have some web server listening at 80 port then you would need stop them or select another port before launch net cat ;-)
P.s.: You need netcat tool installed



12. Allows system wide changes: 
<code>su</code>


13. Converts a single FLAC (or APE) file with associated cue file into multiple FLAC files: <code>cuebreakpoints "$2" | shnsplit -o flac "$1"</code>
Requires:
- cuetools
- shntools



14. Add the ID3 tags in a cue file to the flac files: 
<code>cuetag *.cue *.flac ;</code>Requires:
- cuetools


15. Extract audio stream from an AVI file using mencoder: 
<code>mencoder "${file}" -of rawaudio -oac mp3lame -ovc copy -o audio/"${file/%avi/mp3}"</code>


16. Capture video of a linux desktop: 
<code>ffmpeg -f x11grab -s wxga -r 25 -i :0.0 -sameq /tmp/out.mpg</code>


17. Download an entire website: 
<code>wget --random-wait -r -p -e robots=off -U mozilla http://www.example.com</code>
-p parameter tells wget to include all files, including images.
-e robots=off you don't want wget to obey by the robots.txt file
-U mozilla as your browsers identity.
--random-wait to let wget chose a random number of seconds to wait, avoid get into black list.
Other Useful wget Parameters:
--limit-rate=20k limits the rate at which it downloads files.
-b continues wget after logging out.
-o $HOME/wget_log.txt logs the output


18. Kill: a process that is locking a file: 
<code>fuser -k filename</code>


19. Don't miss the next PI or 234567890 day, find out current unix time: 
<code>date +%s</code>


20. Scans for open ports using telnet:
<code>HOST=127.0.0.1;for((port=1;port<=65535;++port)); do echo -en "$port ";if echo -en "open $HOST $port\nlogout\quit"  |  telnet 2>/dev/null |  grep 'Connected to' > /dev/null; then echo -en "\n\nport $port/tcp is open\n\n";fi;done | grep open</code>