sshcopyid option: exit if `ssh-add -L` fails to execute

If a user requested the --sshcopyid option then it's supposed
to be run successfully, otherwise it might leave an inaccessible
system, so exit with error if execution of `ssh-add -L` fails.

While at it:

* simplify code (no need for $RC)
* don't fail if directory /root/.ssh exists already
* append keys to possibly existing /root/.ssh/authorized_keys
  file, instead of overwriting it

diff --git a/grml-debootstrap b/grml-debootstrap
index a87dbab..d5c3f70 100755 (executable)
--- a/grml-debootstrap
+++ b/grml-debootstrap
@@ -1764,16 +1764,21 @@ iface ${interface} inet dhcp
   fi
 
   if [ -n "${SSHCOPYID}" ] ; then
-    ssh-add -L > /dev/null 2>&1 ; RC=$?
-    if [ $RC -eq 0 ] ; then
+    if ssh-add -L >/dev/null 2>&1 ; then
       einfo "Use locally available public keys to authorise root login on the target system as requested via --sshcopyid option."
-      mkdir "${MNTPOINT}"/root/.ssh
+      mkdir -p "${MNTPOINT}"/root/.ssh
       chmod 0700 "${MNTPOINT}"/root/.ssh
-      ssh-add -L > "${MNTPOINT}"/root/.ssh/authorized_keys
-      eend 0
+      if ssh-add -L >> "${MNTPOINT}"/root/.ssh/authorized_keys ; then
+        eend 0
+      else
+        eerror "Error: executing 'ssh-add -L' failed."
+        eend 1
+        bailout 1
+      fi
     else
-      ewarn "Could not open a connection to your authentication agent or the agent has no identites."
-      eend $?
+      eerror "Could not open a connection to your authentication agent or the agent has no identites."
+      eend 1
+      bailout 1
     fi
   fi