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Generate a random password 30 characters long

Terminal - Generate a random password 30 characters long
strings /dev/urandom | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo
2009-02-16 00:39:28
User: jbcurtis
Functions: grep head strings tr
44
Generate a random password 30 characters long

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.

Alternatives

There are 5 alternatives - vote for the best!

Terminal - Alternatives
pwgen -Bs 10 1
2009-12-01 14:33:51
14

-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

< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c6
2009-02-24 09:43:40
User: Blackbit
Functions: head tr
11

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`

gpg --gen-random --armor 1 30
2011-07-20 15:32:49
User: atoponce
Functions: gpg
9

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).

cat /dev/urandom | tr -dc A-Za-z0-9 | head -c 32
pwgen 30 1
2011-07-24 19:43:48
User: sairon
6

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]

Know a better way?

If you can do better, submit your command here.

What others think

Add punctuation to the character set by using '[[:alnum:][:punct:]]' in the grep command.

Comment by hypatiafu 265 weeks and 3 days 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
Comment by hypatiafu 265 weeks and 3 days ago

I prefer http://sourceforge.net/projects/pwgen/ for generating random passwords. Shorter and more flexible.

Comment by Confusion 264 weeks and 5 days ago

I like apg: http://www.adel.nursat.kz/apg/

Comment by renich 264 weeks and 1 day ago

of course you can use a pre-built application, but if you did, you wouldn't be exercising your command-line-fu!

Comment by hypatiafu 263 weeks and 4 days ago

Doesn't seem to do anything on Mac OS X 10.5

Comment by tamouse 258 weeks and 4 days ago

cat /dev/urandom | strings | grep -o '[[:alnum:]]' | head -n 30 | tr -d '\n'; echo

works on Macs

Comment by tamouse 258 weeks and 4 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.

Comment by bubo 256 weeks and 5 days ago

strings: Warning: '/dev/urandom' is not an ordinary file

Comment by hm2k 233 weeks and 6 days ago

' grep -io [[:alnum:]] ' may be much faster than -o only

Comment by mhoudg 160 weeks and 4 days ago

Your point of view

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