Difference between revisions of "Simple loop"

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This HOWTO describes how to dump a very simple shell scripts that just loops and shows that it's alive.
+
This HOWTO describes how to dump a trivial program.
  
−
First of all, if you try to simply launch such program and dump it crtools will  fail. This is because the program you launch from shell shared session and terminal with the shell itself, but crtools should make sure, that no resources are used by external processes. So this simple test would be a little bit trickier, that just it.
+
== Simplest case ==
 +
 
 +
=== Prepare ===
 +
 
 +
Let's create a shell script which loops and reports time every second:
  
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== Dumping a simplest process in a new session without control terminal ==
 
−
* For that we can create a shell script, which will report date and time every second. For removing dependencies on a current terminal it will be executed in a new session and output will be redirected in a file.
 
 
  $ cat > test.sh <<-EOF
 
  $ cat > test.sh <<-EOF
 
  #!/bin/sh
 
  #!/bin/sh
Line 12: Line 14:
 
  done
 
  done
 
  EOF
 
  EOF
−
 
 
  $ chmod +x test.sh
 
  $ 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 &
 
  $ setsid ./test.sh  < /dev/null &> test.log &
 
  [2] 2220
 
  [2] 2220
 
  [2]+  Done                    setsid ./test.sh < /dev/null &>test.log
 
  [2]+  Done                    setsid ./test.sh < /dev/null &>test.log
  
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* Get pid of the test process:
+
=== Dump ===
 +
 
 +
Get the PID of the test process:
 +
 
 
  $  ps -C test.sh
 
  $  ps -C test.sh
 
   PID TTY          TIME CMD
 
   PID TTY          TIME CMD
 
  2221 ?        00:00:00 test.sh
 
  2221 ?        00:00:00 test.sh
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* Dump the test process.
+
 
−
  $  ~/crtools/crtools dump -t 2221 -vvv -o dump.log && echo OK
+
Dump it:
 +
 
 +
  # crtools dump -t 2221 -vvv -o dump.log && echo OK
 
  OK
 
  OK
−
* The state of the processes are saved in a few files:
+
 
 +
=== Check dump files ===
 +
 
 +
The state of the process(es) is saved to a few files:
 +
 
 
  $  ls
 
  $  ls
 
  core-2221.img  eventpoll-tfd.img  filelocks-2221.img  inotify.img      netlinksk.img    pipes.img        sigacts-2424.img  test.log
 
  core-2221.img  eventpoll-tfd.img  filelocks-2221.img  inotify.img      netlinksk.img    pipes.img        sigacts-2424.img  test.log
Line 34: Line 51:
 
  eventfd.img    fifo-data.img      ids-2424.img        mm-2221.img      pages-2.img      rlimit-2424.img  signal-s-2424.img  vmas-2221.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
 
  eventpoll.img  fifo.img          inetsk.img          mm-2424.img      pipes-data.img    sigacts-2221.img  sk-queues.img      vmas-2424.img
−
* Restore the test process.
+
 
−
  $ ~/crtools/crtools restore -d -t 2221 -vvv -o restore.log && echo OK
+
=== Restore ===
 +
 
 +
Restore the test process:
 +
 
 +
  # crtools restore -d -t 2221 -vvv -o restore.log && echo OK
 
  OK
 
  OK
  
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== Dumping one shell job ==
+
== A shell job ==
−
Now let's see how to dump the same program when it is just launched from shell without additional setsid-s and stdio-s redirection.
+
 
 +
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 [http://en.wikipedia.org/wiki/Pseudo_terminal Unix98 PTYs].
 +
 
 +
=== Run ===
  
−
For that we need to execute our test script or another program (e.g. "top") from a terminal without redirections. crtools supports only [http://en.wikipedia.org/wiki/Pseudo_terminal Unix98 PTYs].
 
 
  $ ./test.sh
 
  $ ./test.sh
 
  $ ps -C test.sh
 
  $ ps -C test.sh
 
   PID TTY          TIME CMD
 
   PID TTY          TIME CMD
 
   2621 pts/1    00:00:00 test.sh
 
   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.
 
Currently crtools doesn't support a stopped task, so "crtools dump" must be executed from another terminal.
−
  $  ~/crtools/crtools dump -t 2621
+
 
 +
  # 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.
 
  (00.012929) 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.
 
  (00.013111) Error (cr-dump.c:1636): Dumping FAILED.
−
crtools asks to set the option --shell-job, because we try to dump only a part of session and a slave point of a tty pair. It's a common rule to ask a user, if only a part of something is dumped.
+
 
−
  $ ~/crtools/crtools dump -vvvv -o dump.log -t 2621 --shell-job && echo Ok
+
See, crtools asks to set the <code>--shell-job</code>, 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.
−
  Ok
+
 
 +
  # 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
 
  $  ~/crtools/crtools restore -vvvv -o restore.log -t 2621 --shell-job
 
  Fri Apr 12 12:41:09 MSK 2013
 
  Fri Apr 12 12:41:09 MSK 2013

Revision as of 23:10, 12 April 2013

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
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