I've got an icinga2 process running on Linux which, once or twice a day (at unpredictable times) simply disappears and is no longer running. I'm running the process with its -x debug option, but this does not provide any useful information. The log file shows normal operation, and then suddenly there are no more entries in the log and the process is no longer running.
How can I gather more information about why this process is disappearing/crashing?
Related
error: Forever detected script was killed by signal: SIGKILL
I'm running a node app on production with "forever".
Somewhat randomly, it shows these events in the logs, and this is causing requests with lots of backend processing that access a database to just stop, and you then have to re-request and hope that it finishes before the next SIGKILL.
My question is this: under any circumstances could an application exception cause a SIGKILL like this, in the context of forever?
I can't reproduce this locally in my development environment.
ENVIRONMENT:
ubuntu 14.04
memcached
forever
node by itself (no nginx reverse proxy or anything)
connecting to a postgres database to query data
It's really hard to say for sure if the SIGKILL's are on an set interval, or if they are happening at a certain point in program execution. The logs don't have a timestamp by default. From looking at the output, I'd say it is happening somewhat randomly in program execution since it is at different points in the log file they appear.
Check your system logs to see if the linux kernel's out of memory killer is sending the signal as per this answer
I am very much new to linux and to this forum. I am working on one issue for a customer where they have 10+ Red Hat Linux 5.5 64 bits servers. They want to stop the tomcat process using the stop script (the script uses 'kill -15')
On some servers, the script works fine and stops the tomcat process within seconds.
On some servers, sometimes it stops quickly, sometimes it keeps running for minutes and finally customer has to use 'kill -9' command to stop tomcat. Logs are not indicating anything.
Do you have any idea why there is an intermittent behaviour of this script? How can we catch it in logs etc?
Processes may ignore the SIGTERM(15) signal.
From Wikipedia: http://en.wikipedia.org/wiki/Unix_signal
The SIGTERM signal is sent to a process to request its termination. Unlike the SIGKILL signal, it can be caught and interpreted or ignored by the process. This allows the process to perform nice termination releasing resources and saving state if appropriate.
If it's ignored the only option left is to kill it with SIGKILL(9) which can't be ignored.
Background:
I had an issue with my Rails server recently where it would stop responding, requiring a bounce to get it back up and running. This issue was due to a controller that does some forking upon receiving a POST, to do some heavy-weight concurrent processing -- server response time kept increasing until the server completely stopped responding. I'm pretty sure I have fixed that issue (DB connections copied upon fork weren't getting closed in child processes), but it would be great to authoritatively test that.
Question:
Is there a way to monitor open file descriptors from inside my Rails app? It's running on Linux, so I've been mucking around with the proc filesystem and the lsof command to observe the open file descriptors; this is messy, because it only gives you a snapshot of the current processes. Ideally I would like to print the open file descriptors in the parent and child processes before, during, and after the processing, to ensure that file descriptors don't stay open past their welcome.
One method to consider (probably the simplest) is using a background worker of some sort, such as with Workling, and making it run lsof in intervals, and getting output using syntax:
`lsof | grep something` # shell command example.
Programs like lsof can really hurt performance if run too frequently. Perhaps every 10s to 30s. Perhaps down to maybe 5s, but that's really pushing it. I'm assuming you have a dedicated server or a beasty virtual machine.
In your background worker, you can store these command results into a variable, or grep it down to what you're really looking for (as demonstrated), and access/manipulate the data as you please.
My system includes a task which opens a network socket, receives pushed data from the network, processes it, and writes it out to disk or pings other machines depending on the messages. This task is intended to run forever, and the service is designed to have this task always running. But sometimes it crashes.
What's the best practice for keeping a task like this alive? Assume it's okay for the task to be dead for up to 30 seconds before we restart it.
Some obvious ideas include having a watchdog process that checks to make sure the process is still running. Watchdog could be triggered by cron. But how does it know if the process is alive or not? Write a pidfile? touch a heartbeat file? An ideal solution wouldn't continuously spin up more processes if the machine gets bogged down to the point where the watchdog is running faster than the heartbeat.
Are there standard linux tools for this? I can imagine a solution that uses a message queue, but I'm not sure if that's a good idea or not.
Depending on the nature of the task that you wish to monitor, one method is to write a simple wrapper to start up your task in a fork().
The wrapper task can then do a waitpid() on the child and restart it if it is terminated.
This does depend on modifying the source for the task that you wish to run.
sysvinit will restart processes that die, if added to inittab.
If you're worried about the process freezing without crashing and ending the process, you can use a heartbeat and hard kill the active instance, letting init restart it.
You could use monit along with daemonize. There are lots of tools for this in the *nix world.
Supervisor was designed precisely for this task. From the project website:
Supervisor is a client/server system that allows its users to monitor and control a number of processes on UNIX-like operating systems.
It runs as a daemon (supervisord) controlled by a command line tool, supervisorctl. The configuration file contains a list of programs it is supposed to monitor, among other settings.
The number of options is quite extensive, -- have a look at the docs for a complete list. In your case, the relevant configuration section might be something like this:
[program:my-network-task]
command=/bin/my-network-task # where your binary lives
autostart=true # start when supervisor starts?
autorestart=true # restart automatically when stopped?
startsecs=10 # consider start successful after how many secs?
startretries=3 # try starting how many times?
I have used Supervisor myself and it worked really well once everything was set up. It requires Python, which should not be a big deal in most environments but might be.
I have a daemon process which does the configuration management. all the other processes should interact with this daemon for their functioning. But when I execute a large action, after few hours the daemon process is unresponsive for 2 to 3 hours. And After 2- 3 hours it is working normally.
Debugging utilities for Linux process hang issues?
How to get at what point the linux process hangs?
strace can show the last system calls and their result
lsof can show open files
the system log can be very effective when log messages are written to track progress. Allows to box the problem in smaller areas. Also correlate log messages to other messages from other systems, this often turns up interesting results
wireshark if the apps use sockets to make the wire chatter visible.
ps ax + top can show if your app is in a busy loop, i.e. running all the time, sleeping or blocked in IO, consuming CPU, using memory.
Each of these may give a little bit of information which together build up a picture of the issue.
When using gdb, it might be useful to trigger a core dump when the app is blocked. Then you have a static snapshot which you can analyze using post mortem debugging at your leisure. You can have these triggered by a script. The you quickly build up a set of snapshots which can be used to test your theories.
One option is to use gdb and use the attach command in order to attach to a running process. You will need to load a file containing the symbols of the executable in question (using the file command)
There are a number of different ways to do:
Listening on a UNIX domain socket, to handle status requests. An external application can then inquire as to whether the application is still ok. If it gets no response within some timeout period, then it can be assumed that the application being queried has deadlocked or is dead.
Periodically touching a file with a preselected path. An external application can look a the timestamp for the file, and if it is stale, then it can assume that the appliation is dead or deadlocked.
You can use the alarm syscall repeatedly, having the signal terminate the process (use sigaction accordingly). As long as you keep calling alarm (i.e. as long as your program is running) it will keep running. Once you don't, the signal will fire.
You can seamlessly restart your process as it dies with fork and waitpid as described in this answer. It does not cost any significant resources, since the OS will share the memory pages.