Linux in a Nutshell, Fourth Edition

Name

update

Synopsis

                  update [options]

System administration command. update is a daemon that controls how often the kernel’s disk buffers are flushed to disk. update is also known as bdflush. The daemon forks a couple of processes to call system functions flush( ) and sync( ). When called by an unprivileged user, no daemon is created. Instead, update calls sync( ) and then exits. By default, update will wake up every 5 seconds and flush( ) some dirty buffers. If that doesn’t work, it will try waking up every 30 seconds to sync( ) the buffers to disk. Not all of the listed options are available in every version of update.

Options

-d

Display the kernel parameters. This does not start the update daemon.

-f seconds

Call flush( ) at this interval. Default is 5.

-h

Help. Print a command summary.

-s seconds

Call sync( ) at this interval. Default is 30.

-0 percent

Flush buffers when the specified percent of the buffer cache is dirty.

-1 blocks

The maximum number of dirty blocks to write out per wake cycle.

-2 buffers

The number of clean buffers to try to obtain each time the free buffers are refilled.

-3 blocks

Flush buffers if dirty blocks exceed blocks when trying to refill the buffers.

-4 percent

Percent of buffer cache to scan when looking for free clusters.

-5 seconds

Time for a data buffer to age before being flushed.

-6 seconds

Time for a nondata buffer to age before being flushed.

-7 constant

The time constant to use for load average.

-8 ratio

How low the load average can be before ...