[Users] cat /dev/urandom | head hangs in OVZ 7 CT

[jjs - mainphrame]

I was running the setup script for a program in a new OVZ7 Centos CT, and
it hung forever.

The line where it hung was this:

password=`cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1`

I ran the following command in various environments:

time cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1

In an ordinary physical host, a VM, an OVZ host, and in an LXD container,
the results are as follows:

root at akita:~#  time cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 |
head -n 1
EozLZFPO0nu9UXR77LR6veKodVT9vYNW

real 0m0.008s
user 0m0.003s
sys 0m0.004s
root at akita:~#

But in any OVZ 7 CT, the following occurs:

root at dbserv:~# time cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 |
head -n 1
YtdP0ZUlfNKX1Vlh0VaBVZmO894HbsEp
< hang indefinitely, or until CTRL-C>
^C

real 4m36.571s
user 1m54.928s
sys 4m51.873s
root at dbserv:~#

Interestingly, the problem does not seem to be with /dev/urandom, as the
output is generated immediately. But the process does not end after being
piped into 'head -1'.

So, for whatever reason, the behavior of this one liner is very different
inside an OVZ 7 CT than it is anywhere else.

Your thoughts?

Jake
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