path: root/Documentation/sysrq.txt
diff options
authorEric Sandeen <sandeen@redhat.com>2009-03-31 15:23:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-04-01 08:59:17 -0700
commitc2d7543851849a6923680cdd7e1047ed1a84a1c5 (patch)
treebf3038819d4be83a1d1e64d7b95bbb3d9d908544 /Documentation/sysrq.txt
parent55a63998b8967615a15e2211ba0ff3a84a565824 (diff)
filesystem freeze: allow SysRq emergency thaw to thaw frozen filesystems
Now that the filesystem freeze operation has been elevated to the VFS, and is just an ioctl away, some sort of safety net for unintentionally frozen root filesystems may be in order. The timeout thaw originally proposed did not get merged, but perhaps something like this would be useful in emergencies. For example, freeze /path/to/mountpoint may freeze your root filesystem if you forgot that you had that unmounted. I chose 'j' as the last remaining character other than 'h' which is sort of reserved for help (because help is generated on any unknown character). I've tested this on a non-root fs with multiple (nested) freezers, as well as on a system rendered unresponsive due to a frozen root fs. [randy.dunlap@oracle.com: emergency thaw only if CONFIG_BLOCK enabled] Signed-off-by: Eric Sandeen <sandeen@redhat.com> Cc: Takashi Sato <t-sato@yk.jp.nec.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/sysrq.txt')
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt
index 9e592c718afb..afa2946892da 100644
--- a/Documentation/sysrq.txt
+++ b/Documentation/sysrq.txt
@@ -81,6 +81,8 @@ On all - write a character to /proc/sysrq-trigger. e.g.:
'i' - Send a SIGKILL to all processes, except for init.
+'j' - Forcibly "Just thaw it" - filesystems frozen by the FIFREEZE ioctl.
'k' - Secure Access Key (SAK) Kills all programs on the current virtual
console. NOTE: See important comments below in SAK section.
@@ -160,6 +162,9 @@ t'E'rm and k'I'll are useful if you have some sort of runaway process you
are unable to kill any other way, especially if it's spawning other
+"'J'ust thaw it" is useful if your system becomes unresponsive due to a frozen
+(probably root) filesystem via the FIFREEZE ioctl.
* Sometimes SysRq seems to get 'stuck' after using it, what can I do?
That happens to me, also. I've found that tapping shift, alt, and control