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NAME |
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Sys::FreezeThaw - stop and start all user processes on a machine |
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|
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SYNOPSIS |
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use Sys::FreezeThaw; |
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|
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Sys::FreezeThaw::freezethaw { |
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# run code while system is frozen |
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}; |
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|
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my $token = Sys::FreezeThaw::freeze; |
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... do something ... |
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Sys::FreezeThaw::thaw $token; |
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|
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DESCRIPTION |
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Operating Systems/Kernels current supported: Linux-2.6/3.0 with /proc. |
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|
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This module implements a very specific feature: stopping(freezing and |
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thawing/continuing all userspace processes on the machine. It works by |
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sending SIGSTOP to all processes, parent-process first, so that the wait |
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syscall will not trigger on stopped children. Restarting is done in |
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reverse order. |
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|
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Using the combined function Sys::FreezeThaw::freezethaw is recommended |
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as it will catch runtime errors, but stopping and restarting can be dine |
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via separate function calls. |
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|
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What could it possibly be sueful for?? |
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Possible uses include: doing atomic file system operations (such as |
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replacing files while they are guaranteed not to be in use), or quieting |
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down a system to investigate suspicious behaviour. |
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|
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Sys::FreezeThaw::freezethaw { BLOCK } |
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First tries to stop all processes. If successful, runs the given |
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code block (or code reference), then restarts all processes again. |
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As the system is basically frozen during the code block execution, |
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it should be as fast as possible. |
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|
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Runtime errors will be caught with "eval". If an exception occurs it |
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will be re-thrown after processes are restarted. If processes cannot |
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be frozen or restarted, this function will throw an exception. |
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|
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Signal handlers for SIGINT, SIGTERM, SIGPIPE, SIGHUP, SIGALRM, |
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SIGUSR1 and SIGUSR2 will be installed temporarily, so if you want to |
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catch these, you have to do so yourself within the executed code |
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block. |
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|
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Try to do as few things as possible. For example, outputting text |
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might cause a deadlock, as the terminal emulator on the other side |
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of STDOUT might be stopped, logging to syslog might not work and so |
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on. |
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|
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The return value of the code block is ignored right now, and the |
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function doesn't yet return anything sensible. |
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|
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$token = Sys::FreezeThaw::freeze |
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Send SIGSTOP to all processes, and return a token that allows them |
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to be thawed again. |
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|
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If an error occurs, an exception will be thrown and all stopped |
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processes will automatically be thawed. |
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|
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Sys::FreezeThaw::thaw $token |
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Take a token returned by Sys::FreezeThaw::freeze and send all |
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processes a "CONT" signal, in the order required for them not to |
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receive child STOP notifications. |
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|
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$Sys::FreezeThaw::PARTIAL_OK |
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A boolean that tells "freeze" whether it is an error if a process |
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cannot be stopped. If false (the default), then "freeze" will fail |
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if there is an unstoppable process. If it is true, then "freeze" |
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will pretend it the process stopped. |
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|
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BUGS |
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SIGCONT is not unnoticed by processes. Some programs (such as |
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irssi-text) respond by flickering (IMHO a bug in irssi-text). Other |
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programs might have other problems, but actual problems should be rare. |
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However, one shouldn't overuse this module. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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