Simple loop
This HOWTO describes how to dump a trivial program.
Simplest case
Prepare
Let's create a shell script which loops and reports time every second:
$ cat > test.sh <<-EOF #!/bin/sh while :; do sleep 1 date done EOF $ chmod +x test.sh
Run (isolated)
Now, if you try to simply run and try to dump such a program, crtools will fail. The reason is a program you launch from the shell shares some common resources with the shell, notably its session and terminal. Crtools has a built-in check that makes sure there are no such resources.
To remove the dependency on a current terminal, let's executed our script in a new session and redirect its output to a file:
$ setsid ./test.sh < /dev/null &> test.log & [2] 2220 [2]+ Done setsid ./test.sh < /dev/null &>test.log
Dump
Get the PID of the test process:
$ ps -C test.sh PID TTY TIME CMD 2221 ? 00:00:00 test.sh
Dump it:
# crtools dump -t 2221 -vvv -o dump.log && echo OK OK
Check dump files
The state of the process(es) is saved to a few files:
$ ls core-2221.img eventpoll-tfd.img filelocks-2221.img inotify.img netlinksk.img pipes.img sigacts-2424.img test.log core-2424.img fanotify.img filelocks-2424.img inotify-wd.img packetsk.img pstree.img signalfd.img test.sh creds-2221.img fanotify-mark.img fs-2221.img inventory.img pagemap-2221.img reg-files.img signal-p-2221.img tty.img creds-2424.img fdinfo-2.img fs-2424.img itimers-2221.img pagemap-2424.img remap-fpath.img signal-p-2424.img tty-info.img dump.log fdinfo-3.img ids-2221.img itimers-2424.img pages-1.img rlimit-2221.img signal-s-2221.img unixsk.img eventfd.img fifo-data.img ids-2424.img mm-2221.img pages-2.img rlimit-2424.img signal-s-2424.img vmas-2221.img eventpoll.img fifo.img inetsk.img mm-2424.img pipes-data.img sigacts-2221.img sk-queues.img vmas-2424.img
Restore
Restore the test process:
# crtools restore -d -t 2221 -vvv -o restore.log && echo OK OK
A shell job
Now let's see how to dump the same program when it is just started from the shell without any additional setsid and stdio redirection. For that we need to execute our test script or another program (e.g. "top") from a terminal without any redirection.
Note crtools only supports Unix98 PTYs.
Run
$ ./test.sh $ ps -C test.sh PID TTY TIME CMD 2621 pts/1 00:00:00 test.sh
Dump
Currently crtools doesn't support a stopped task, so "crtools dump" must be executed from another terminal.
# crtools dump -t 2621 (00.012929) Error (tty.c:1022): tty: Found dangling tty with sid 940 pgid 2621 (pts) on peer fd 0. Consider using --shell-job option. (00.013111) Error (cr-dump.c:1636): Dumping FAILED.
See, crtools asks to set the --shell-job
, because we try to dump only a part of a session and a slave end of a tty pair. It is a common rule to ask a user, if only a part of something is dumped.
# crtools dump -vvvv -o dump.log -t 2621 --shell-job && echo OK OK
Restore
$ ~/crtools/crtools restore -vvvv -o restore.log -t 2621 --shell-job Fri Apr 12 12:41:09 MSK 2013 Fri Apr 12 12:41:10 MSK 2013