| View previous topic :: View next topic |
| Author |
Message |
zbindere
Guru
Joined: 27 May 2004
Posts: 356
Location: Switzerland
|
 Posted: Wed Feb 16, 2005 11:45 am Post subject: ssh daemon crashed, I am screwed [actually not crashed] |
 |
|
I run at home a webserver. now the ssh daemon crashed. this is already the second time this happens. I don't have any keyboard, mouse, monitor attached. so I have to reboot the server.
are there other solutions? how could I restart the ssh daemon maybe using a web-inerface? I don't want to run a telnet server as backup. does someone have similar problems?
Last edited by zbindere on Wed Feb 16, 2005 2:06 pm; edited 1 time in total |
|
| Back to top |
|
 |
jh294
n00b
Joined: 27 Jan 2004
Posts: 13
Location: Toronto, Canada
|
| Posted: Wed Feb 16, 2005 12:30 pm Post subject: RE: ssh daemon crashed, I am screwed |
|
|
You have a few choices:
1) The obvious and recommended solution is to determine why SSHD is crashing and fix it.
2) Start a second instance of the SSH daemon listening on another port. If the first one is not responding, use the second one. This may or may not help depending on the cause of the crash. There is no reason to limit yourself to only a second instance, you can easily run three, four or more daemons all listening on different ports. Please see option 1.
3) Restart SSH every 10 minutes from cron. You will not impact current sessions just new connections during the restart (1 to 3 seconds depending on your system). This may or may not help matters and could possibly result in problems with cron and process table. Please see option 1.
Good luck.
_________________
--
If XP is the answer, you didn't understand the question. |
|
| Back to top |
|
|
cselkirk
Apprentice
Joined: 09 Jun 2003
Posts: 199
Location: NL
|
| Posted: Wed Feb 16, 2005 12:37 pm Post subject: |
|
|
I would be more inclined to want to know why is crashes, nothing in /var/log/messages? Anyhow, you could run something like the following from crontab, which will restart sshd if the test string is empty (note the "[s]shd", specificly the "[s]", is there to stop the ps returning itself).
| Code: | #!/bin/sh
if [[ -z $(ps aux |grep /usr/sbin/[s]shd) ]]; then
/etc/init.d/sshd restart
fi |
HTH
_________________
cn=cselkirk,dc=xs4all,dc=nl |
|
| Back to top |
|
|
zbindere
Guru
Joined: 27 May 2004
Posts: 356
Location: Switzerland
|
| Posted: Wed Feb 16, 2005 12:52 pm Post subject: |
|
|
thanks all. I checked /var/log/messages. no entries.
I think I will do the cron thing. this is the easiest since this does not happen very often. |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 1:06 pm Post subject: |
|
|
| cselkirk wrote: | I
| Code: | #!/bin/sh
if [[ -z $(ps aux |grep /usr/sbin/[s]shd) ]]; then
/etc/init.d/sshd restart
fi |
HTH |
If this doesn't work try putting quotes (" ") around the grep argument like so:
| Code: |
if [[ -z $(ps aux |grep "/usr/sbin/[s]shd") ]]; then
|
I tried the 'ps' statement on the commandline and it wouldn't work correctly without the quotes. |
|
| Back to top |
|
|
cselkirk
Apprentice
Joined: 09 Jun 2003
Posts: 199
Location: NL
|
| Posted: Wed Feb 16, 2005 1:10 pm Post subject: |
|
|
As this machine is world accessable and providing world accessable services I would be somewhat suspicious of the fact this happens, particularly as openssh is, in my experience, not prone to crashing. How do you know it's actually crashing? (given that you are unable to login and check). The fact that you are unable to access port 22 could mean a number of things (firewall rules affecting the specific host and/or subnet you are loging in from for example). There are various things that could be at fault and I would be less inclined to write it off to "ssh crashing" before looking into the problem further.
_________________
cn=cselkirk,dc=xs4all,dc=nl |
|
| Back to top |
|
|
cselkirk
Apprentice
Joined: 09 Jun 2003
Posts: 199
Location: NL
|
| Posted: Wed Feb 16, 2005 1:25 pm Post subject: |
|
|
| SilverOne wrote: | | I tried the 'ps' statement on the commandline and it wouldn't work correctly without the quotes. |
huh?
| Code: | zsh% print $SHELL
zsh
zsh% ps aux |grep /usr/sbin/[s]shd
root 19495 0.0 0.1 3136 1328 ? Ss Feb12 0:00 /usr/sbin/sshd
zsh% /bin/bash -
bash# ps aux |grep /usr/sbin/[s]shd
root 19495 0.0 0.1 3136 1328 ? Ss Feb12 0:00 /usr/sbin/sshd
bash# exit
zsh% print "just to make sure it's nothing from my env" >> /dev/null
zsh% /bin/ps aux | /bin/grep /usr/sbin/[s]shd
root 19495 0.0 0.1 3136 1328 ? Ss Feb12 0:00 /usr/sbin/sshd |
_________________
cn=cselkirk,dc=xs4all,dc=nl |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 1:30 pm Post subject: |
|
|
Well this is the output I get:
| Code: |
# ps aux | grep /usr/sbin/[s]shd
root 13358 0.0 0.2 3644 1440 ? Ss Jan21 0:01 /usr/sbin/sshd
root 30973 0.0 0.1 1464 872 pts/0 R+ 14:28 0:00 grep /usr/sbin/sshd
# ps aux | grep "/usr/sbin/[s]shd"
root 13358 0.0 0.2 3644 1440 ? Ss Jan21 0:01 /usr/sbin/sshd
#
|
I'm running bash.
I've got no idea why our outputs differ. |
|
| Back to top |
|
|
j-m
Retired Dev
Joined: 31 Oct 2004
Posts: 975
|
| Posted: Wed Feb 16, 2005 1:37 pm Post subject: |
|
|
| SilverOne wrote: |
I'm running bash.
I've got no idea why our outputs differ. |
Do you have bash-3.0  |
|
| Back to top |
|
|
lookinin
Guru
Joined: 21 Jan 2005
Posts: 486
|
| Posted: Wed Feb 16, 2005 1:38 pm Post subject: |
|
|
My bash does the same - grep outputs itself... why not try pidof?
| Code: | pidof sshd
if [ $? -eq 0 ]
then
echo running
else
echo not running
fi |
|
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 1:46 pm Post subject: |
|
|
| j-m wrote: | | SilverOne wrote: |
I'm running bash.
I've got no idea why our outputs differ. |
Do you have bash-3.0 |
Nope:
| Code: |
* app-shells/bash
Latest version available: 2.05b-r9
Latest version installed: 2.05b-r9
|
|
|
| Back to top |
|
|
j-m
Retired Dev
Joined: 31 Oct 2004
Posts: 975
|
| Posted: Wed Feb 16, 2005 1:51 pm Post subject: |
|
|
| SilverOne wrote: | | j-m wrote: |
Do you have bash-3.0 |
Nope:
|
OK. I have, but it also does not work without quotation marks; I like the pidof version better anyway...  |
|
| Back to top |
|
|
cselkirk
Apprentice
Joined: 09 Jun 2003
Posts: 199
Location: NL
|
| Posted: Wed Feb 16, 2005 1:58 pm Post subject: |
|
|
| SilverOne wrote: | | I've got no idea why our outputs differ. |
I had thought maybe zsh was behaving differently, which is why I also tested under bash. What does the following give you?
| Code: | | env -i /bin/ps aux | /bin/grep /usr/sbin/[s]shd |
My guess is it's something in your env.
_________________
cn=cselkirk,dc=xs4all,dc=nl |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 2:06 pm Post subject: |
|
|
| cselkirk wrote: |
My guess is it's something in your env. |
Might've been but that doesn't appear to be so....
| Code: |
# env -i /bin/ps aux | /bin/grep /usr/sbin/[s]shd
root 13358 0.0 0.2 3644 1440 ? Ss Jan21 0:01 /usr/sbin/sshd
root 6826 0.0 0.1 1480 868 pts/5 R+ 15:05 0:00 /bin/grep /usr/sbin/sshd
# env -i /bin/ps aux | /bin/grep "/usr/sbin/[s]shd"
root 13358 0.0 0.2 3644 1440 ? Ss Jan21 0:01 /usr/sbin/sshd
#
|
What's your Bash version? Or does this have to do with process management? |
|
| Back to top |
|
|
lookinin
Guru
Joined: 21 Jan 2005
Posts: 486
|
| Posted: Wed Feb 16, 2005 2:07 pm Post subject: |
|
|
| cselkirk wrote: | | Code: | | env -i /bin/ps aux | /bin/grep /usr/sbin/[s]shd |
|
The output of that is the same - but here's another idea:
| Code: | | # ps aux | grep [s]shd |
|
|
| Back to top |
|
|
zbindere
Guru
Joined: 27 May 2004
Posts: 356
Location: Switzerland
|
| Posted: Wed Feb 16, 2005 2:09 pm Post subject: |
|
|
cselkirk: you were right.
I actually could get in again. my company changed the hostname of the gw.
I use tcpwrappres to limit access to the ssh service so that was the error.
sorry for that  |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 2:11 pm Post subject: |
|
|
| lookinin wrote: | but here's another idea:
| Code: | | # ps aux | grep [s]shd |
|
Indeed, that skips the 'grep' statement in the process list. (anybody know why??)
It does however list all instances of SSHD that are handling logged-in users.
The fact that users are logged in is no certain indication of a running SSH daemon. |
|
| Back to top |
|
|
lookinin
Guru
Joined: 21 Jan 2005
Posts: 486
|
| Posted: Wed Feb 16, 2005 2:19 pm Post subject: |
|
|
| SilverOne wrote: | | Indeed, that skips the 'grep' statement in the process list. (anybody know why??) |
Because now the grep expression is actually [s]shd, so [s] prevents it from matching because the first character is a bracket
| SilverOne wrote: | It does however list all instances of SSHD that are handling logged-in users.
The fact that users are logged in is no certain indication of a running SSH daemon. |
Unintended side effect - I was just looking for something that worked with grep
Wow, phpBB really did not like my first version of this reply 
Last edited by lookinin on Wed Feb 16, 2005 2:21 pm; edited 1 time in total |
|
| Back to top |
|
|
jh294
n00b
Joined: 27 Jan 2004
Posts: 13
Location: Toronto, Canada
|
| Posted: Wed Feb 16, 2005 2:20 pm Post subject: |
|
|
| SilverOne wrote: | | cselkirk wrote: |
My guess is it's something in your env. |
Might've been but that doesn't appear to be so....
What's your Bash version? Or does this have to do with process management? |
Different shells interpret control/meta characters differently and therefore require different quoting. In the case of BASH, the shell tries to interpret the metecharacter prior to passing it to grep. To prevent this, quotes are required. An aternative that will work in either bash or zsh shells is:
| Code: |
ps aux | grep /usr/bin/sshd | grep -v grep
|
_________________
--
If XP is the answer, you didn't understand the question. |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 2:23 pm Post subject: |
|
|
| lookinin wrote: |
Unintended side effect - I was just looking for something that worked with grep
|
Try this (I took your idea and found this:)
| Code: | | # ps aux | grep [/]usr/sbin/sshd |
| lookinin wrote: |
Wow, phpBB really did not like my first version of this reply |
No it didn't but I understood what you meant  |
|
| Back to top |
|
|
cselkirk
Apprentice
Joined: 09 Jun 2003
Posts: 199
Location: NL
|
| Posted: Wed Feb 16, 2005 2:24 pm Post subject: |
|
|
| SilverOne wrote: | | Indeed, that skips the 'grep' statement in the process list. (anybody know why??) |
Yes, with the "[s]" the grep will be looking for the regular expression "[s]shd" and as [s]shd is not "sshd" it won't show up in what is returned by grep. More specificly "[]" is a grep regular expression meaning "any single character in the bracketed list".
_________________
cn=cselkirk,dc=xs4all,dc=nl |
|
| Back to top |
|
|
j-m
Retired Dev
Joined: 31 Oct 2004
Posts: 975
|
| Posted: Wed Feb 16, 2005 2:26 pm Post subject: |
|
|
| jh294 wrote: |
| Code: |
ps aux | grep /usr/bin/sshd | grep -v grep
|
|
Umm... No. Nothing. Nada. Zero...  |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 2:29 pm Post subject: |
|
|
| cselkirk wrote: |
Yes, with the "[s]" the grep will be looking for the regular expression "[s]shd" and as [s]shd is not "sshd" it won't show up in what is returned by grep. More specificly "[]" is a grep regular expression meaning "any single character in the bracketed list". |
Well I know something about regex's so I got the meaning of [s]. What I did not grasp was why [s]shd (which indeed skipped the grep process) was treated differently than /usr/bin/[s]shd (which showed up as /usr/bin/sshd in the grep process). The first expression is interpreted like we expected, and the second wasn't (well only on cselkirk's machine).
Perhaps different versions of grep? (don't think so, but I've got no ideas left.)
| Code: |
# grep --version
grep (GNU grep) 2.5.1
|
|
|
| Back to top |
|
|
lookinin
Guru
Joined: 21 Jan 2005
Posts: 486
|
| Posted: Wed Feb 16, 2005 2:30 pm Post subject: |
|
|
| Quote: | Try this (I took your idea and found this:)
| Code: | | # ps aux | grep [/]usr/sbin/sshd |
|
Yes, that works nicely.
| Quote: | | It does however list all instances of SSHD that are handling logged-in users. |
I just wanted to mention that pidof will also do this. |
|
| Back to top |
|
|
SilverOne
Apprentice
Joined: 10 Nov 2003
Posts: 161
|
| Posted: Wed Feb 16, 2005 2:33 pm Post subject: |
|
|
| j-m wrote: | | jh294 wrote: |
| Code: |
ps aux | grep /usr/bin/sshd | grep -v grep
|
|
Umm... No. Nothing. Nada. Zero... |
Try changin /usr/bin/sshd to /usr/sbin/sshd
It works for me then. |
|
| Back to top |
|
|
|
Networking & Security
