Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual page 71

Each of these values defines a different rule for dealing with error messages. The first value, called
the console loglevel, defines the lowest priority of messages printed to the console. (Note that, the
lower the priority, the higher the loglevel number.) The second value sets the default loglevel for
messages without an explicit loglevel attached to them. The third value sets the lowest possible
loglevel configuration for the console loglevel. The last value sets the default value for the console
loglevel.
• random/ directory — Lists a number of values related to generating random numbers for the
kernel.
• rtsig-max — Configures the maximum number of POSIX real-time signals that the system may
have queued at any one time. The default value is 1024.
• rtsig-nr — Lists the current number of POSIX real-time signals queued by the kernel.
• sem — Configures semaphore settings within the kernel. A semaphore is a System V IPC object
that is used to control utilization of a particular process.
• shmall— Sets the total amount of shared memory pages that can be used at one time, system-
wide. By default, this value is 2097152.
• shmmax — Sets the largest shared memory segment size allowed by the kernel, in bytes. By
default, this value is 33554432. However, the kernel supports much larger values than this.
• shmmni — Sets the maximum number of shared memory segments for the whole system, in bytes.
By default, this value is 4096
• sysrq — Activates the System Request Key, if this value is set to anything other than zero (0), the
default.
The System Request Key allows immediate input to the kernel through simple key combinations.
For example, the System Request Key can be used to immediately shut down or restart a system,
sync all mounted file systems, or dump important information to the console. To initiate a System
Request Key, type Alt+SysRq+<system request code> . Replace <system request
code> with one of the following system request codes:
• r — Disables raw mode for the keyboard and sets it to XLATE (a limited keyboard mode which
does not recognize modifiers such as Alt, Ctrl, or Shift for all keys).
• k — Kills all processes active in a virtual console. Also called Secure Access Key (SAK), it is
often used to verify that the login prompt is spawned from init and not a trojan copy designed to
capture usernames and passwords.
• b — Reboots the kernel without first unmounting file systems or syncing disks attached to the
system.
• c — Crashes the system without first unmounting file systems or syncing disks attached to the
system.
• o — Shuts off the system.
• s — Attempts to sync disks attached to the system.
• u — Attempts to unmount and remount all file systems as read-only.
/proc/sys/
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