Unfortunately, this section contains more conjectures and questions than facts. Perhaps you can help?
If you issue the ps aux command, you will see something like the following:
USER PID %CPU %MEM SIZE RSS TTY STAT START TIME COMMAND root 1 0.1 8.0 1284 536 ? S 07:37 0:04 init [2] root 2 0.0 0.0 0 0 ? SW 07:37 0:00 (kflushd) root 3 0.0 0.0 0 0 ? SW 07:37 0:00 (kupdate) root 4 0.0 0.0 0 0 ? SW 07:37 0:00 (kpiod) root 5 0.0 0.0 0 0 ? SW 07:37 0:00 (kswapd) root 52 0.0 10.7 1552 716 ? S 07:38 0:01 syslogd -m 0 root 54 0.0 7.1 1276 480 ? S 07:38 0:00 klogd root 56 0.3 17.3 2232 1156 1 S 07:38 0:13 -bash root 57 0.0 7.1 1272 480 2 S 07:38 0:01 /sbin/agetty 38400 tt root 64 0.1 7.2 1272 484 S1 S 08:16 0:01 /sbin/agetty -L ttyS1 root 70 0.0 10.6 1472 708 1 R Sep 11 0:01 ps aux
This is a list of the processes running on the system. Note that init
is process number one. Processes 2, 3, 4 and 5 are kflushd, kupdate, kpiod and
kswapd. There is something strange here though: notice that in both the virtual
storage size (SIZE) and the Real Storage Size (RSS) columns, these processes
have zeroes. How can a process use no memory? These processes are really part
of the kernel. The kernel does not show up on process lists at all, and you can
only work out what memory it is using by subtracting the memory available from
the amount on your system. The brackets around the command name could signify
that these are kernel processes(?)
kswapd moves parts of programs that are not currently being used
from real storage (ie RAM) to the swap space (ie hard disk). kflushd
writes data from buffers to disk. This allows things to run faster. What
programs write can be kept in memory, in a buffer, then written to disk in
larger more efficient chunks. I don't know what kupdate and
kpiod are for.
This is where my knowledge ends. What do these last two daemons do? Why do kernel daemons get explicit process numbers rather than just being anonymous bits of kernel code? Does init actually start them, or are they already running when init arrives on the scene?
I put a script to mount /proc and do a ps aux in /sbin/init. Process 1 was the script itself, and processess 2, 3, 4 and 5 were the kernel daemons just as under the real init. The kernel must put these processes there, because my script certainly didn't!
I don't know of any configuration for these kernel daemons.
Find out what these processes are for, how they work, and write a new ``Kernel Daemons'' section for this document and send it to me!
The Linux Documentation Project's ``The Linux Kernel'' (see The Linux Kernel for url), and the kernel source code are all I can think of.