The ERRORS section could be clearer as to what error you get when you try to lock a socket/fifo.
- todd Index: lib/libc/gen/lockf.3 =================================================================== RCS file: /cvs/src/lib/libc/gen/lockf.3,v retrieving revision 1.13 diff -u -p -u -r1.13 lockf.3 --- lib/libc/gen/lockf.3 5 Jun 2013 03:39:22 -0000 1.13 +++ lib/libc/gen/lockf.3 25 Jun 2019 15:10:47 -0000 @@ -201,7 +201,8 @@ and the section is already locked by ano .It Bq Er EBADF The argument .Fa filedes -is not a valid open file descriptor. +is not a valid open file descriptor or it +refers to an object other than a file. .Pp The argument .Fa function Index: lib/libc/sys/flock.2 =================================================================== RCS file: /cvs/src/lib/libc/sys/flock.2,v retrieving revision 1.20 diff -u -p -u -r1.20 flock.2 --- lib/libc/sys/flock.2 10 Dec 2014 19:19:00 -0000 1.20 +++ lib/libc/sys/flock.2 25 Jun 2019 15:09:27 -0000 @@ -133,7 +133,9 @@ The argument .Fa operation has an invalid value. .It Bq Er EOPNOTSUPP -The referenced descriptor is not of the correct type. +The argument +.Fa fd +refers to an object other than a file. .El .Sh SEE ALSO .Xr close 2 , Index: lib/libc/sys/fcntl.2 =================================================================== RCS file: /cvs/src/lib/libc/sys/fcntl.2,v retrieving revision 1.32 diff -u -p -u -r1.32 fcntl.2 --- lib/libc/sys/fcntl.2 10 Nov 2018 11:54:03 -0000 1.32 +++ lib/libc/sys/fcntl.2 25 Jun 2019 15:13:45 -0000 @@ -427,7 +427,7 @@ segment of a file to be locked is alread exclusive-locked by another process. .It Bq Er EBADF .Fa fd -is not a valid open file descriptor. +is not a valid open file descriptor or is not of the correct type. .Pp The argument .Fa cmd
