/dev/urandom

wikipedia:urandom

 head -10 /dev/urandom | sha512sum | cut -b 1-30

https://github.com/coreutils/coreutils/blob/master/NEWS

 shred, sort, shuf: now use an internal pseudorandom generator by default.
 This is mainly noticeable in shred where the 3 random passes it does by
 default should proceed at the speed of the disk.  Previously /dev/urandom
 was used if available, which is relatively slow on GNU/Linux systems.

See also

• Random, /dev/urandom
• oathtool