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A colleague suggested creating a random key via the following command:

tr -dc A-Za-z0-9_\!\@\#\$\%\^\&\*\(\)-+= < /dev/urandom | head -c 32 | xargs

It gave me the error:

tr: Illegal byte sequence

I'm concerned that I do not have /dev/urandom on my system. I tried googling to figure out how to install this file, but I have come up empty. I tried locate urandom and also came up empty. (well actually, it found the man page, but that doesn't help)

How do I make urandom available on my Mac OSX system? (Lion)

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Interesting use of xargs... – sendmoreinfo May 16 at 19:41

3 Answers

up vote 8 down vote accepted

Based on the error message that you get, I don't think /dev/urandom is the problem. If it were, I'd expect an error like "no such file or directory".

I searched for the error message you got and found this, which seems like it might be relevant to your issue: http://nerdbynature.de/s9y/?176

Basically, specify the locale by prepending the tr command with LC_CTYPE=C:

LC_CTYPE=C tr -dc A-Za-z0-9_\!\@\#\$\%\^\&\*\(\)-+= < /dev/urandom | head -c 32 | xargs
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Thanks, that indeed did the trick. Any idea why I cannot find urandom or random? Are they special magical "files" that don't exist on the actual filesystem? (Also I suggested an edit to help mitigate link-rot) – Kirk Woll Aug 13 '12 at 18:53
I believe locate doesn't directly search your filesystem, but rather looks up your query using a pre-built database. This database is most likely configured to ignore /dev/ and other 'special' filesystems. – lk- Aug 13 '12 at 19:01
fair enough, but I don't see it when I look directly in /dev. Go figure. But thanks again for the help. – Kirk Woll Aug 13 '12 at 19:04
up vote 0 down vote

According to the man page, /dev/random is probably going to be sufficient for your needs. Perhaps Apple ceased to create the /dev/urandom because it is unnecessary?

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I do not have /dev/random either. – Kirk Woll Aug 13 '12 at 18:23
MacOSX should have both /dev/random and /dev/urandom. Perhaps Apple no longer includes those special files anymore? Or maybe it's only there if you install XCode? – jsbillings Aug 13 '12 at 18:36
FWIW, both devices are present on my Lion-upgraded-to-Mountain Lion workstation. I believe it was present on Lion, as well. Nodes are different as well (13,0 vs. 13,1) – mrb Aug 13 '12 at 18:41
up vote 2 down vote

Your tr attempts to interpret its input as text in UTF-8 encoding. So it will complain and abort upon the first byte sequence which is not valid UTF-8. Prefixing tr with LC_ALL=C or LC_CTYPE=C will export that variable into the environment of tr, thus changing its idea of the local character set to the C standard, i.e. everything is just a sequence of opaque bytes.

By the way, is the sequence \)-+ in your command intentional? This includes * as well, which you already included, but does not include - itself as you might have intended. Better to write one of these instead:

LC_ALL=C tr -dc 'A-Za-z0-9_!@#$%^&*()\-+=' < /dev/urandom
LC_CTYPE=C tr -dc A-Za-z0-9_\!\@\#\$\%\^\&\*\(\)\\-+= < /dev/urandom
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