How to put in order a command through ssh from one MT on another?
Here so does not work (to the user it is authorised to come without the password)

/system ssh 192.168.100.126 user=test
:delay 2
:log error TESTERROR
/quit


Thanks.

ssh 192.168.100.126 -l test ":log error TESTERROR"
or
ssh test@192.168.100.126 ":log error TESTERROR"

I have found it only works from shell on remote computer. ssh in the MT routers will not work with this.

[admin@VPN] > system ssh test@192.168.100.126 ":log error TESTERROR"
expected end of command (line 1 column 33)

As he indicated you cannot execute remote commands from the router shell. Its SSH client doesn't support it.