strace:
execve("./wzdftpd", ["./wzdftpd"], [/* 33 vars */]) = 0
Process 17996 attached (waiting for parent)
Process 17996 resumed (parent 17995 ready)
Process 17995 detached
Process 17997 attached
Process 18001 attached
Process 18002 attached (waiting for parent)
Process 18002 resumed (parent 18001 ready)
Process 18001 suspended
[pid 18002] execve("/opt/wzdftpd/bin/test.sh", ["/opt/wzdftpd/bin/test.sh"], [/* 0 vars */]) = 0
Process 18001 resumed
Process 18002 detached
[pid 17996] --- SIGCHLD (Child exited) @ 0 (0) ---

lftp:
lftp wzdftpd@localhost:~> site mytest
`SITE mytest' at 0 [Waiting for response...]

wzd.log:
Nov 14 10:30:44 Initializing TLS (this can take a while).
Nov 14 10:30:44 TLS initialization successful.
Nov 14 10:30:44 nl_langinfo: ISO-8859-1
Nov 14 10:30:44 UTF-8 detected and enabled
Nov 14 10:30:44 DEBUG Checking library version
Nov 14 10:30:44 DEBUG: binding to ip 2502
Nov 14 10:30:45 mysql connection is not crypted.
Nov 14 10:30:45 INFO starting crontab
Nov 14 10:30:45 Process 17996 ok
Nov 14 10:30:45 wzdftpd Linux mt 0.9.0 started (build 20071113)
Nov 14 10:30:45 Waiting for connections (main)
Nov 14 10:30:58 DEBUG IPv4 connection accepted
Nov 14 10:30:58 Connection opened from 127.0.0.1 (socket 0)
Nov 14 10:30:58 error sending ident request Connection refused
Nov 14 10:30:58 Client speaking to socket 0
Nov 14 10:30:58 control connection succesfully switched to ssl (cipher: AES128-SHA)
Nov 14 10:30:58 DEBUG registered uid 1 with backend 1
Nov 14 10:30:58 DEBUG registered gid 1 with backend 1
Nov 14 10:30:58 WARNING: empty password field whould not be allowed !
Nov 14 10:30:58 WARNING: you should run: UPDATE users SET userpass='%' WHERE userpass is NULL
Nov 14 10:30:58 LOGIN OKAY from localhost
Nov 14 10:30:58 Wed Nov 14 10:30:58 2007 LOGIN: localhost (127.0.0.1) "wzdftpd" "admin" "local admin"
Nov 14 10:30:58 DEBUG parse_ftp_command("PWD")
Nov 14 10:30:58 DEBUG parse_ftp_command("PBSZ 0")
Nov 14 10:30:58 DEBUG parse_ftp_command("TYPE I")
Nov 14 10:30:58 DEBUG parse_ftp_command("SITE mytest")
Nov 14 10:30:58 INFO calling external command [/opt/wzdftpd/bin/test.sh]
Nov 14 10:30:58 DEBUG spawned process 18002 exited with status 0

test.sh:
/opt/wzdftpd/bin$ cat test.sh
#!/bin/sh
echo "200 hello"
exit 0

wzd.cfg:
site_mytest = /opt/wzdftpd/bin/test.sh