|
⇤ ← Revision 1 as of 2007-05-02 23:57:17
Size: 1930
Comment:
|
Size: 1932
Comment: converted to 1.6 markup
|
| Deletions are marked like this. | Additions are marked like this. |
| Line 1: | Line 1: |
| [[Anchor(faq63)]] | <<Anchor(faq63)>> |
| Line 9: | Line 9: |
| This is a "feature" of [http://www.openssh.org/ OpenSSH]. The client will not close the connection as long as the remote end's terminal still is still in use -- and in the case of {{{sleep 120 &}}}, stdout and stderr are still connected to the terminal. | This is a "feature" of [[http://www.openssh.org/|OpenSSH]]. The client will not close the connection as long as the remote end's terminal still is still in use -- and in the case of {{{sleep 120 &}}}, stdout and stderr are still connected to the terminal. |
My ssh client hangs when I try to run a remote background job!
The following will not do what you expect:
ssh me@remotehost 'sleep 120 &' # Client hangs for 120 seconds
This is a "feature" of OpenSSH. The client will not close the connection as long as the remote end's terminal still is still in use -- and in the case of sleep 120 &, stdout and stderr are still connected to the terminal.
The immediate answer to your question -- "How do I get the client to disconnect so I can get my shell back?" -- is to kill the ssh client. You can do this with the kill or pkill commands, of course; or by sending the INT signal (usually Ctrl-C) for a non-interactive ssh session (as above); or by pressing <Enter><~><.> (Enter, Tilde, Period) in the client's terminal window for an interactive remote shell.
The long-term workaround for this is to ensure that all the file descriptors are redirected to a log file (or /dev/null) on the remote side:
ssh me@remotehost 'sleep 120 >/dev/null 2>&1 &' # Client should return immediately
This also applies to restarting daemons on some legacy Unix systems.
ssh root@hp-ux-box # Interactive shell ... # Discover that the problem is stale NFS handles /sbin/init.d/nfs.client stop # autofs is managed by this script and /sbin/init.d/nfs.client start # killing it on HP-UX is OK (unlike Linux) exit # Client hangs -- use Enter ~ . to kill it.
The legacy Unix /sbin/init.d/nfs.client script runs daemons in the background but leaves their stdout and stderr attached to the terminal (and they don't fully self-daemonize). The solution is either to fix the Unix vendor's broken init script, or to kill the ssh client process after this happens. The author of this article uses the latter approach.