On 10/22/2013 12:53 PM, Dan Bassett wrote:
First off, we've got two openvz environments running. Both are on CentOS6, our
production environment is on vzctl 4.2.1 and our test is on 4.5.1. With that
stuff out of the way…
If I start a console on a container using vzctl, then detach, then start that
same console again, the console remains blank. This seems to be the default
(and possibly intended) behavior, but it seems kind of lame. If I (or more
importantly, a user) has left something like a vi session running and they get
disconnected and then come back, the vi session doesn't redraw when the console
gets reattached. In most cases, our users aren't clueful enough to deal with
this situation and they just assume that something is broken.
This is what Ctrl-L in vim is for.
Alternatively, you can use ESC ! to kill everything running on current
console (so-called SAK,
http://en.wikipedia.org/wiki/Secure_attention_key) so it will revert to
show usual getty screen (if configured). In the first vzctl console
implementation we did SAK on exit, so every vzctl console started with a
fresh session (if init is configured to run getty on it). Unfortunately,
some programs got attached to /dev/console so we removed SAK on exit.
I have found that if I enter the container or attach on some other tty and
cause a SIGWINCH to be generated and sent to the foreground process in the tty
in question, it happily redraws itself. This has worked for vi, emacs, less
and bash so far (and I expect other to work as well).
vzctl console sends SIGWINCH upon attaching. The problem is neither bash
nor vim react to it, probably because the window size is still the same.
But if you do vzctl console, run vim (or bash), detach, change the xterm
size and run another vzctl console, you will see that vim/bash redraws.
My crappy way around this is to use stty inside the container to get the
number of columns, then set the number of columns to one less than that value,
then set it back to the original value. Oddly, just using kill to send a
SIGWINCH to the foreground process doesn't always work. Unfortunately, I
haven't come up with a good way of causing this action to happen when a user
connects with vzctl console...
The only thing I can think of is a dirty hack -- on attach, send one
SIGWINCH with a different (bogus) window size, then another one with a
proper size. Same crappy way as you found, just automated.
Attached patch does just that -- and it works for me. Please give it a
try and report back.
Nevertheless, this looks a big ugly to me.
Anyway, before everybody says "Just use ssh!", I should make it clear that
connecting with ssh in our environment isn't always possible. We're using openvz to
teach systems administration, so we start with a container that doesn't have any
networking set up or the sshd package installed. Therefore, the only option is to have
students connect on the consoles until they have networking set up.
Well, in fact neither vzctl console (nor vzctl enter) were meant to be
used this way. vzctl console is more like a way to see how system boots
(because init writes to the console), vzctl enter is a backdoor. So
So finally my question. Am I missing something here, or is this just the way
it is? I wanted to make sure I wasn't missing something obvious before I
emailed the developer list to ask if anything could be done. Thanks!
diff --git a/src/enter.c b/src/enter.c
index 0bc4f74..c297b1a 100644
--- a/src/enter.c
+++ b/src/enter.c
@@ -414,8 +414,16 @@ static void console_winch(int sig)
if (ioctl(0, TIOCGWINSZ, &ws))
warn("Unable to get window size");
- else if (ioctl(tty, TIOCSWINSZ, &ws))
- warn("Unable to set window size");
+ else {
+ if (sig == 0) { /* just attached */
+ /* force a redraw by "changing" the term size */
+ ws.ws_row++;
+ ioctl(tty, TIOCSWINSZ, &ws);
+ ws.ws_row--;
+ }
+ if (ioctl(tty, TIOCSWINSZ, &ws))
+ warn("Unable to set window size");
+ }
}
static void sak(void)
@@ -455,7 +463,7 @@ int do_console_attach(vps_handler *h, envid_t veid, int ttyno)
signal(SIGCHLD, child_handler);
signal(SIGWINCH, console_winch);
- console_winch(SIGWINCH);
+ console_winch(0);
fprintf(stderr, "Attached to CT %d (ESC . to detach)\n", veid);
if ((pid = fork()) < 0) {
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