Lsof can be blocked by some kernel functions that it uses -
lstat(2), readlink(2), and stat(2). These functions are stalled
in the kernel, for example, when the hosts where mounted NFS file
systems reside become inaccessible.
Lsof attempts to break these blocks with timers and child
processes, but the techniques are not wholly reliable. When lsof
does manage to break a block, it will report the break with an
error message. The messages may be suppressed with the -t and -w
options.
The default timeout value may be displayed with the -h or -?
option, and it may be changed with the -S [t] option. The
minimum for t is two seconds, but you should avoid small values,
since slow system responsiveness can cause short timeouts to
expire unexpectedly and perhaps stop lsof before it can produce
any output.
When lsof has to break a block during its access of mounted file
system information, it normally continues, although with less
information available to display about open files.
Lsof can also be directed to avoid the protection of timers and
child processes when using the kernel functions that might block
by specifying the -O option. While this will allow lsof to start
up with less overhead, it exposes lsof completely to the kernel
situations that might block it. Use this option cautiously.
