summaryrefslogtreecommitdiffstats
path: root/Documentation/sysctl
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/sysctl')
-rw-r--r--Documentation/sysctl/fs.txt17
-rw-r--r--Documentation/sysctl/kernel.txt60
-rw-r--r--Documentation/sysctl/vm.txt4
3 files changed, 60 insertions, 21 deletions
diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt
index 1458448436c..62682500878 100644
--- a/Documentation/sysctl/fs.txt
+++ b/Documentation/sysctl/fs.txt
@@ -96,13 +96,16 @@ handles that the Linux kernel will allocate. When you get lots
of error messages about running out of file handles, you might
want to increase this limit.
-The three values in file-nr denote the number of allocated
-file handles, the number of unused file handles and the maximum
-number of file handles. When the allocated file handles come
-close to the maximum, but the number of unused file handles is
-significantly greater than 0, you've encountered a peak in your
-usage of file handles and you don't need to increase the maximum.
-
+Historically, the three values in file-nr denoted the number of
+allocated file handles, the number of allocated but unused file
+handles, and the maximum number of file handles. Linux 2.6 always
+reports 0 as the number of free file handles -- this is not an
+error, it just means that the number of allocated file handles
+exactly matches the number of used file handles.
+
+Attempts to allocate more file descriptors than file-max are
+reported with printk, look for "VFS: file-max limit <number>
+reached".
==============================================================
nr_open:
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 2dbff53369d..a028b92001e 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -22,6 +22,7 @@ show up in /proc/sys/kernel:
- callhome [ S390 only ]
- auto_msgmni
- core_pattern
+- core_pipe_limit
- core_uses_pid
- ctrl-alt-del
- dentry-state
@@ -135,6 +136,27 @@ core_pattern is used to specify a core dumpfile pattern name.
==============================================================
+core_pipe_limit:
+
+This sysctl is only applicable when core_pattern is configured to pipe core
+files to user space helper a (when the first character of core_pattern is a '|',
+see above). When collecting cores via a pipe to an application, it is
+occasionally usefull for the collecting application to gather data about the
+crashing process from its /proc/pid directory. In order to do this safely, the
+kernel must wait for the collecting process to exit, so as not to remove the
+crashing processes proc files prematurely. This in turn creates the possibility
+that a misbehaving userspace collecting process can block the reaping of a
+crashed process simply by never exiting. This sysctl defends against that. It
+defines how many concurrent crashing processes may be piped to user space
+applications in parallel. If this value is exceeded, then those crashing
+processes above that value are noted via the kernel log and their cores are
+skipped. 0 is a special value, indicating that unlimited processes may be
+captured in parallel, but that no waiting will take place (i.e. the collecting
+process is not guaranteed access to /proc/<crahing pid>/). This value defaults
+to 0.
+
+==============================================================
+
core_uses_pid:
The default coredump filename is "core". By setting
@@ -313,31 +335,43 @@ send before ratelimiting kicks in.
==============================================================
+printk_delay:
+
+Delay each printk message in printk_delay milliseconds
+
+Value from 0 - 10000 is allowed.
+
+==============================================================
+
randomize-va-space:
This option can be used to select the type of process address
space randomization that is used in the system, for architectures
that support this feature.
-0 - Turn the process address space randomization off by default.
+0 - Turn the process address space randomization off. This is the
+ default for architectures that do not support this feature anyways,
+ and kernels that are booted with the "norandmaps" parameter.
1 - Make the addresses of mmap base, stack and VDSO page randomized.
This, among other things, implies that shared libraries will be
- loaded to random addresses. Also for PIE-linked binaries, the location
- of code start is randomized.
+ loaded to random addresses. Also for PIE-linked binaries, the
+ location of code start is randomized. This is the default if the
+ CONFIG_COMPAT_BRK option is enabled.
- With heap randomization, the situation is a little bit more
- complicated.
- There a few legacy applications out there (such as some ancient
+2 - Additionally enable heap randomization. This is the default if
+ CONFIG_COMPAT_BRK is disabled.
+
+ There are a few legacy applications out there (such as some ancient
versions of libc.so.5 from 1996) that assume that brk area starts
- just after the end of the code+bss. These applications break when
- start of the brk area is randomized. There are however no known
+ just after the end of the code+bss. These applications break when
+ start of the brk area is randomized. There are however no known
non-legacy applications that would be broken this way, so for most
- systems it is safe to choose full randomization. However there is
- a CONFIG_COMPAT_BRK option for systems with ancient and/or broken
- binaries, that makes heap non-randomized, but keeps all other
- parts of process address space randomized if randomize_va_space
- sysctl is turned on.
+ systems it is safe to choose full randomization.
+
+ Systems with ancient and/or broken binaries should be configured
+ with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
+ address space randomization.
==============================================================
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index faf62740aa2..a6e360d2055 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -624,7 +624,9 @@ caching of directory and inode objects.
At the default value of vfs_cache_pressure=100 the kernel will attempt to
reclaim dentries and inodes at a "fair" rate with respect to pagecache and
swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
-to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
+to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
+never reclaim dentries and inodes due to memory pressure and this can easily
+lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
causes the kernel to prefer to reclaim dentries and inodes.
==============================================================