grep hogs entire cpu Post: 302591037

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Special Forums UNIX and Linux Applications grep hogs entire cpu Post 302591037 by Corona688 on Wednesday 18th of January 2012 11:19:39 AM

01-18-2012

Registered User

Server distributions often lower the tick rate so pre-emption happens less often, but it'd be ridiculous to turn it off. Anyone who's ever used windows 3.1 knows the consequences of that, and allowing one faulty usermode process to bomb your system is beyond stupid. I don't accept that option means what you think it does. I'll investigate in more detail myself.

There's an enormous problem with your explanation, anyway. His system did, in fact, pre-empt grep. How else could he have regained control by ctrl-alt-f1? Why would it pre-empt for ctrl-alt-f1, and not for the GUI? His system wasn't hardlocked. The GUI had malfunctioned.

---------- Post updated at 10:19 AM ---------- Previous update was at 08:51 AM ----------

I'm pretty sure you're talking about kernel-mode pre-emption, which is something different. It allows the kernel to pre-empt itself in some circumstances so it can respond more quickly and smoothly to realtime requests. This is often left disabled for servers, because it may trade some performance for response time.

This has nothing to do with the pre-emption of user-mode programs. A linux system that lacks user-mode pre-emption would not be stable or sane.

So I stand by my earlier point: grep should not have been able to freeze a system by consuming 100% CPU. Something else is going wrong with this system. If this is the system I think it is, COKEDUDE has had strange problems with this system before, like random segmentation faults in perfectly good programs, so I don't trust that grep itself is the issue.

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xfs_freeze

xfs_freeze(8)						      System Manager's Manual						     xfs_freeze(8)

NAME

       xfs_freeze - suspend access to an XFS filesystem

SYNOPSIS

       xfs_freeze -f | -u mount-point

DESCRIPTION

       xfs_freeze suspends and resumes access to an XFS filesystem (see xfs(5)).

       xfs_freeze  halts  new access to the filesystem and creates a stable image on disk.  xfs_freeze is intended to be used with volume managers
       and hardware RAID devices that support the creation of snapshots.

       The mount-point argument is the pathname of the directory where the filesystem is mounted.  The filesystem must be  mounted  to	be  frozen
       (see mount(8)).

       The  -f flag requests the specified XFS filesystem to be frozen from new modifications.	When this is selected, all ongoing transactions in
       the filesystem are allowed to complete, new write system calls are halted, other calls which modify the	filesystem  are  halted,  and  all
       dirty data, metadata, and log information are written to disk.  Any process attempting to write to the frozen filesystem will block waiting
       for the filesystem to be unfrozen.

       Note that even after freezing, the on-disk filesystem can contain information on files that are still in the process of	unlinking.   These
       files will not be unlinked until the filesystem is unfrozen or a clean mount of the snapshot is complete.

       The  -u	flag  is used to un-freeze the filesystem and allow operations to continue.  Any filesystem modifications that were blocked by the
       freeze are unblocked and allowed to complete.

       One of -f or -u must be supplied to xfs_freeze.

NOTES

       A copy of a frozen XFS filesystem will usually have the same universally unique identifier (UUID) as the original, and  thus  may  be  pre-
       vented from being mounted.  The XFS nouuid mount option can be used to circumvent this issue.

       In  Linux  kernel version 2.6.29, the interface which XFS uses to freeze and unfreeze was elevated to the VFS, so that this tool can now be
       used on many other Linux filesystems.

SEE ALSO

       xfs(5), lvm(8), mount(8).

																     xfs_freeze(8)