Generate a random password 30 characters long

strings /dev/urandom | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo
Find random strings within /dev/urandom. Using grep filter to just Alphanumeric characters, and then print the first 30 and remove all the line feeds.
Sample Output
user@machine:~$ strings /dev/urandom | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo
XhJjKL07KNZSDDpwdPm9rACnW3FR0w

50
By: jbcurtis
2009-02-16 00:39:28

15 Alternatives + Submit Alt

  • -B flag = don't include characters that can be confused for other characters (this helps when you give someone their password for the first time so they don't cause a lockout with, for example, denyhosts or fail2ban) -s flag = make a "secure", or hard-to-crack password -y flag = include special characters (not used in the example because so many people hate it -- however I recommend it) "1 10" = output 1 password, make it 10 characters in length For even more secure passwords please use the -y flag to include special characters like so: pwgen -Bsy 10 1 output>> }&^Y?.>7Wu Show Sample Output


    15
    pwgen -Bs 10 1
    linuxrawkstar · 2009-12-01 14:33:51 1
  • If you want a password length longer than 6, changing the -c6 to read -c8 will give you 8 random characters instead of 6. To end up with a line-feed, use this with echo: # echo `< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c6`


    11
    < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c6
    Blackbit · 2009-02-24 09:43:40 4
  • According to the gpg(1) manual: --gen-random 0|1|2 count Emit count random bytes of the given quality level 0, 1 or 2. If count is not given or zero, an endless sequence of random bytes will be emitted. If used with --armor the output will be base64 encoded. PLEASE, don't use this command unless you know what you are doing; it may remove precious entropy from the system! If your entropy pool is critical for various operations on your system, then using this command is not recommended to generate a secure password. With that said, regenerating entropy is as simple as: du -s / This is a quick way to generate a strong, base64 encoded, secure password of arbitrary length, using your entropy pool (example above shows a 30-character long password). Show Sample Output


    10
    gpg --gen-random --armor 1 30
    atoponce · 2011-07-20 15:32:49 2

  • 9
    cat /dev/urandom | tr -dc A-Za-z0-9 | head -c 32
    noqqe · 2011-11-20 17:29:45 0
  • The pwgen program generates passwords which are designed to be easily memorized by humans, while being as secure as possible. Human-memorable passwords are never going to be as secure as completely completely random passwords. [from pwgen man page] Show Sample Output


    6
    pwgen 30 1
    sairon · 2011-07-24 19:43:48 0

What Others Think

Add punctuation to the character set by using '[[:alnum:][:punct:]]' in the grep command.
hypatiafu · 487 weeks and 1 day ago
OK, this is what I settled on to remove ambiguous characters: strings /dev/urandom | grep -o '[[:graph:]]' | grep '[^0O1l]' | head -n 20 | tr -d '\n'; echo
hypatiafu · 487 weeks and 1 day ago
I prefer http://sourceforge.net/projects/pwgen/ for generating random passwords. Shorter and more flexible.
Confusion · 486 weeks and 3 days ago
I like apg: http://www.adel.nursat.kz/apg/
renich · 485 weeks and 6 days ago
of course you can use a pre-built application, but if you did, you wouldn't be exercising your command-line-fu!
hypatiafu · 485 weeks and 2 days ago
Doesn't seem to do anything on Mac OS X 10.5
tamouse · 480 weeks and 2 days ago
cat /dev/urandom | strings | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo works on Macs
tamouse · 480 weeks and 2 days ago
i usually use this one: cat /dev/urandom | tr -cd 0-9a-zA-Z | head -c 30 it's short and comes handy in scripts, e.g. asigning random names for loops etc.
bubo · 478 weeks and 2 days ago
strings: Warning: '/dev/urandom' is not an ordinary file
hm2k · 455 weeks and 4 days ago
' grep -io [[:alnum:]] ' may be much faster than -o only
mhoudg · 382 weeks and 2 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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