Hi,
I installed a new version of GNU coreutils (9.3), and now "shuf" appears
to be blocking on Linux's cryptographic RNG init. On this particular
machine, there is not a lot of entropy sources so Linux's RNG init takes
an unbounded and potentially very long time.
I hope nobody expects "shuf" to provide cryptographically-secure
randomness (I certainly don't), and it would be nice for shuf to
not hang indefinitely.
Running with strace I see shuf makes two calls to getrandom, the
first passes the GRND_NONBLOCK flag, and shuf appears to fall back to
using clock_gettime in this case, but the second call passes 0 for flags
which means "block until RNG init", and this is the one that hangs.
shuf only makes the second getrandom call if there is actually input
(so shuf </dev/null is OK).
When it is working, after RNG init, strace shows the problematic call
(but it is successful in this case):
% echo x | strace ./shuf 2>&1 | grep getrandom
% getrandom("\xd5\x55\xc9\x73", 4, GRND_NONBLOCK) = 4
% getrandom("\x76", 1, 0) = 1
note the 0 flags in the second call. When it is not working (before RNG
init), the second call hangs indefinitely (killed by a signal in this
case):
% echo x | strace ./shuf 2>&1
[...]
getrandom(0xb6f148c8, 4, GRND_NONBLOCK) = -1 EAGAIN (Resource
temporarily unavailable)
clock_gettime64(CLOCK_MONOTONIC, 0xbed4e810) = -1 ENOSYS (Function
not implemented)
clock_gettime(CLOCK_MONOTONIC, {tv_sec=270, tv_nsec=854650394}) = 0
[...]
getrandom(0x1c40228, 1, 0) = ? ERESTARTSYS (To be
restarted if SA_RESTART is set)
--- SIGINT {si_signo=SIGINT, si_code=SI_KERNEL} ---
+++ killed by SIGINT +++
I do not have this problem with coreutils 8.28. Using the GNU-specific
--random-source=/dev/urandom option is a possible workaround (since
/dev/urandom reads do not block).
Let me know if you need any more info.
Thanks,
Nick
