how to debug when xinetd says : got signal 17 (child exited)

Question

I am trying to start services vsftpd and sshd using xinetd. my config files are as follows.

1. /etc/xinetd.conf

   defaults
   {
   instances               = 60
   log_type                = FILE /var/log/xinetdlog
   log_on_success          = HOST PID
   log_on_failure          = HOST
   cps                     = 25 30
   only_from       = localhost
   }
   includedir /etc/xinetd.d
   

2. /etc/xinetd.d/ftp

   service ftp
   {
   disable = no
   server = /usr/sbin/vsftpd
   server_args = -l
   user = root
   socket_type = stream
   protocol = tcp
   wait = no
   instances = 4
   flags = REUSE
   nice = 10
   log_on_success      += DURATION HOST USERID
   only_from = 127.0.0.1 10.0.0.0/24
   }
   

3. /etc/xinetd.d/ssh

   service ssh
   {
   disable = no
   log_on_failure += USERID
   server = /usr/sbin/sshd
   user = root
   socket_type = stream
   protocol = tcp
   wait = no
   instances = 20
   flags = REUSE
   only_from = 127.0.0.1 10.0.0.0/24
   }
   

Even though i've included only_from attribute, vsftp server as well as ssh server are refusing connection from localhost. while vsftp and ssh servers are working fine individually when i check with "service vsftpd start" and "service ssh start". when i did debug using "xinetd -d" throug terminal i got the output as

13/10/20@00:06:08: DEBUG: 3592 {cnf_start_services} Started service: ftp
13/10/20@00:06:08: DEBUG: 3592 {cnf_start_services} Started service: ssh
13/10/20@00:06:08: DEBUG: 3592 {cnf_start_services} mask_max = 8, services_started = 2
13/10/20@00:06:08: NOTICE: 3592 {main} xinetd Version 2.3.14 started with libwrap loadavg options compiled in.
13/10/20@00:06:08: NOTICE: 3592 {main} Started working: 2 available services
13/10/20@00:06:08: DEBUG: 3592 {main_loop} active_services = 2
13/10/20@00:06:16: DEBUG: 3592 {main_loop} select returned 1
13/10/20@00:06:16: DEBUG: 3592 {server_start} Starting service ftp
13/10/20@00:06:16: DEBUG: 3592 {main_loop} active_services = 2
13/10/20@00:06:16: DEBUG: 3607 {exec_server} duping 9
13/10/20@00:06:16: DEBUG: 3592 {main_loop} active_services = 2
13/10/20@00:06:16: DEBUG: 3592 {main_loop} select returned 1
13/10/20@00:06:16: DEBUG: 3592 {check_pipe} Got signal 17 (Child exited)
13/10/20@00:06:16: DEBUG: 3592 {child_exit} waitpid returned = 3607
13/10/20@00:06:16: DEBUG: 3592 {server_end} ftp server 3607 exited
13/10/20@00:06:16: DEBUG: 3592 {svc_postmortem} Checking log size of ftp service
13/10/20@00:06:16: INFO: 3592 {conn_free} freeing connection
13/10/20@00:06:16: DEBUG: 3592 {child_exit} waitpid returned = -1

both services are getting started but neither of them is working.

after banging for 3-4 hours i still don't have any clue about this error. Any help would be appreciated. thanks!

Answer 1

The signal(7) man page says:

Signal     Value     Action   Comment
---------------------------------------------------------
SIGCHLD   20,17,18    Ign     Child stopped or terminated

This means that whenever a child process stops i.e. vsftpd or sshd, the parent - xinetd - receives signal 17 (which would be ignored by default, but in your case it's not).

You also need to start sshd with -i:

-i

Specifies that sshd is being run from inetd(8). sshd is normally not run from inetd because it needs to generate the server key before it can respond to the client, and this may take tens of seconds. Clients would have to wait too long if the key was regenerated every time. However, with small key sizes (e.g. 512) using sshd from inetd may be feasible.

I don't know what vsftpd version you're using, but vsftpd-2.2.2-6.el6_0.1 works fine if I set listen=NO in /etc/vsftpd/vsftpd.conf and run it without any arguments.