ssh: move logic about background processes to VM.start_background_process

We likely never need to launch a background process that way on a windows
machine that is not a VM.  Encapsulating the behaviour at this place will
let us stop having commands.ssh return type depend on `target_os`, which
cannot be properly expressed with type hints because of its non-literal
nature.

Signed-off-by: Yann Dirson <[email protected]>

Author: ydirson

lib/commands.py

@@ -76,17 +76,11 @@ def _ssh(hostname_or_ip, cmd, check, simple_output, suppress_fingerprint_warning
         command = cmd
     else:
         command = " ".join(cmd)
-    if background and target_os != "windows":
-        # https://stackoverflow.com/questions/29142/getting-ssh-to-execute-a-command-in-the-background-on-target-machine
-        # ... and run the command through a bash shell so that output redirection both works on Linux and FreeBSD.
-        # Bash being available on VMs is a documented requirement.
-        command = "nohup bash -c \"%s &>/dev/null &\"" % command
 
     ssh_cmd = f"ssh root@{hostname_or_ip} {' '.join(opts)} {shlex.quote(command)}"
 
-    windows_background = background and target_os == "windows"
     # Fetch banner and remove it to avoid stdout/stderr pollution.
-    if config.ignore_ssh_banner and not windows_background:
+    if config.ignore_ssh_banner:
         banner_res = subprocess.run(
             "ssh root@%s %s '%s'" % (hostname_or_ip, ' '.join(opts), '\n'),
             shell=True,
@@ -102,7 +96,7 @@ def _ssh(hostname_or_ip, cmd, check, simple_output, suppress_fingerprint_warning
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT
     )
-    if windows_background:
+    if background:
         return True, process
 
     stdout = []

lib/vm.py

@@ -271,9 +271,15 @@ def start_background_process(self, cmd):
                 self.sftp_put(f.name, script.replace("/tmp/", "/Users/root/AppData/Local/Temp/"))
             else:
                 self.scp(f.name, script)
-            # Use bash to run the script, to avoid being hit by differences between shells, for example on FreeBSD
+
+            # https://stackoverflow.com/questions/29142/getting-ssh-to-execute-a-command-in-the-background-on-target-machine
+            # ... and run the command through a bash shell so that output redirection both works on Linux and FreeBSD.
             # It is a documented requirement that bash is present on all test VMs.
-            self.ssh(['bash', script], background=True)
+            remote_cmd = f"bash {script}"
+            if not self.is_windows:
+                remote_cmd = f'nohup bash -c "{remote_cmd} &>/dev/null &"'
+            self.ssh(remote_cmd, background=True)
+
             wait_for(lambda: self.ssh_with_result(['test', '-f', pidfile]),
                      "wait for pid file %s to exist" % pidfile)
             pid = self.ssh(['cat', pidfile])