Symptoms
When trying to rsync data between two cPanel servers you may experience a timeout or connection failure.
Description
While these issues wouldn't be related to the cPanel software on the machine, the error message can be helpful to diagnose the issue.
packet_write_wait: Connection to 192.168.0.1 port 22: Broken pipe
rsync: connection unexpectedly closed (104508573 bytes received so far) [receiver]
rsync error: error in rsync protocol data stream (code 12) at io.c(226) [receiver=3.1.2]
rsync: connection unexpectedly closed (104542504 bytes received so far) [generator]
rsync error: unexplained error (code 255) at io.c(226) [generator=3.1.2]
Workaround
rsync has a list of exit codes included in its man page which you can review by typing "man rsync" on any Linux system. You can see the list of codes here:
0 Success
1 Syntax or usage error
2 Protocol incompatibility
3 Errors selecting input/output files, dirs
4 Requested action not supported: an attempt was made to manipulate 64-bit files on a platform that cannot support them; or an option was specified that is supported by the
client and not by the server.
5 Error starting client-server protocol
6 Daemon unable to append to log-file
10 Error in socket I/O
11 Error in file I/O
12 Error in rsync protocol data stream
13 Errors with program diagnostics
14 Error in IPC code
20 Received SIGUSR1 or SIGINT
21 Some error returned by waitpid()
22 Error allocating core memory buffers
23 Partial transfer due to error
24 Partial transfer due to vanished source files
25 The --max-delete limit stopped deletions
30 Timeout in data send/receive
35 Timeout waiting for daemon connection
In the example provided above we see error code 12, which indicates an issue with the data stream. This can be caused by a network issue, disk space problems on either the source or destination server, or data that has went missing from the source machine since the rsync file list was generated.
You could attempt to troubleshoot the issue by disabling the firewall on both severs to see if that helps with the problem. If not, checking to make sure that data isn't being changed on the source while the rsync is happening is a good next step, or there could also be additional networking issues that would need to be investigated outside of your server itself.
If there are still issues after working through this guide it might be helpful to contact a professional systems administrator. There is a list of admins for hire available here that can help.