bessd crashes when it restarts

[sangjinhan]

How to reproduce:

$ bessctl daemon start
$ bessctl daemon start

E1025 00:19:47.651084 63354 bessd.cc:72] read(pidfile=/var/run/bessd.pid): Resource temporarily unavailable [11]
F1025 00:19:47.651481 63354 bessd.cc:97] Couldn't read pidfile: Resource temporarily unavailable [11]
*** Check failure stack trace: ***
@ 0x7fd6f911f5cd google::LogMessage::Fail()
@ 0x7fd6f9121433 google::LogMessage::SendToLog()
@ 0x7fd6f911f15b google::LogMessage::Flush()
@ 0x7fd6f911f379 google::LogMessage::~LogMessage()
@ 0x7fd6f912040a google::ErrnoLogMessage::~ErrnoLogMessage()
@ 0x52f1a7 bess::bessd::TryAcquirePidfileLock()
@ 0x52f224 bess::bessd::CheckUniqueInstance()
@ 0x4b8431 main
@ 0x7fd6f75c9830 __libc_start_main
@ 0x4c0b79 _start
@ (nil) (unknown)
F1025 00:19:47.839265 63353 bessd.cc:183] Failed. (syslog may have details)
*** Check failure stack trace: ***
@ 0x7fd6f911f5cd google::LogMessage::Fail()
@ 0x7fd6f9121433 google::LogMessage::SendToLog()
@ 0x7fd6f911f15b google::LogMessage::Flush()
@ 0x7fd6f9121e1e google::LogMessageFatal::~LogMessageFatal()
@ 0x52f693 bess::bessd::StartDaemon()
@ 0x4b84a5 main
@ 0x7fd6f75c9830 __libc_start_main
@ 0x4c0b79 _start
@ (nil) (unknown)
Aborted (core dumped)
*** Error: Cannot start BESS daemon