Autossh not accepting logfile option for ssh - ssh

Question

autossh -M 10984 -v -o "PubkeyAuthentication=yes" -o "PasswordAuthentication=no" -R 6889:localhost:22 user#rpi.local
The above command works. The one below doesn't.
autossh -M 10984 -E /home/pi/ssh.log -v -o "PubkeyAuthentication=yes" -o "PasswordAuthentication=no" -R 6889:localhost:22 user#rpi.local
It says,
/usr/lib/autossh/autossh: invalid option -- 'E'`
How can I specify a log file as the SSH option when passing it to autossh?

Answer 1

This is a limitation of autossh. The autossh source code contains a list of command-line switches which the program accepts. The list is apparently supposed to include all of the ssh options, but it doesn't include "E":
#define OPTION_STRING "M:V1246ab:c:e:fgi:kl:m:no:p:qstvw:xyACD:F:I:MKL:NO:PR:S:TVXY"
...
/*
* We accept all ssh args, and quietly pass them on
* to ssh when we call it.
*/
while ((ch = getopt(argc, argv, OPTION_STRING)) != -1) {
switch(ch) {
case 'M':
...
It seems there are a few workarounds at present:
Run autossh with standard error directed to the desired file:
autossh -M 10984 -v -o ... user#rpi.local 2>>/some/log/file
SSH instances launched from autossh should inherit the redirection.
Use the ssh "-y" option to log through syslog, and have syslog write the messages where you want them to be written.
Modify the autossh source code to add support for the "-E" option.
Report the issue to the autossh maintainer and hope he fixes it in a later release.