6.t

早期freebsd实现

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.\"	@(#)6.t	8.1 (Berkeley) 7/27/93
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.ds LH "Installing/Operating \*(4B
.ds CF \*(Dy
.Sh 1 "System operation"
.PP
This section describes procedures used to operate a \*(4B UNIX system.
Procedures described here are used periodically, to reboot the system,
analyze error messages from devices, do disk backups, monitor
system performance, recompile system software and control local changes.
.Sh 2 "Bootstrap and shutdown procedures"
.PP
In a normal reboot, the system checks the disks and comes up multi-user
without intervention at the console.
Such a reboot
can be stopped (after it prints the date) with a ^C (interrupt).
This will leave the system in single-user mode, with only the console
terminal active.
(If the console has been marked ``insecure'' in
.Pn /etc/ttys
you must enter the root password to bring the machine to single-user mode.)
It is also possible to allow the filesystem checks to complete
and then to return to single-user mode by signaling
.Xr fsck (8)
with a QUIT signal (^\|\e).
.PP
To bring the system up to a multi-user configuration from the single-user
status,
all you have to do is hit ^D on the console.  The system
will then execute
.Pn /etc/rc ,
a multi-user restart script (and
.Pn /etc/rc.local ),
and come up on the terminals listed as
active in the file
.Pn /etc/ttys .
See
.Xr init (8)
and
.Xr ttys (5) for more details.
Note, however, that this does not cause a filesystem check to be done.
Unless the system was taken down cleanly, you should run
``fsck \-p'' or force a reboot with
.Xr reboot (8)
to have the disks checked.
.PP
To take the system down to a single user state you can use
.DS
\fB#\fP \fIkill 1\fP
.DE
or use the
.Xr shutdown (8)
command (which is much more polite, if there are other users logged in)
when you are running multi-user.
Either command will kill all processes and give you a shell on the console,
as if you had just booted.  Filesystems remain mounted after the
system is taken single-user.  If you wish to come up multi-user again, you
should do this by:
.DS
\fB#\fP \fIcd /\fP
\fB#\fP \fI/sbin/umount -a\fP
\fB#\fP \fI^D\fP
.DE
.PP
Each system shutdown, crash, processor halt and reboot
is recorded in the system log
with its cause.
.Sh 2 "Device errors and diagnostics"
.PP
When serious errors occur on peripherals or in the system, the system
prints a warning diagnostic on the console.
These messages are collected
by the system error logging process
.Xr syslogd (8)
and written into a system error log file
.Pn /var/log/messages .
Less serious errors are sent directly to
.Xr syslogd ,
which may log them on the console.
The error priorities that are logged and the locations to which they are logged
are controlled by
.Pn /etc/syslog.conf .
See
.Xr syslogd (8)
for further details.
.PP
Error messages printed by the devices in the system are described with the
drivers for the devices in section 4 of the programmer's manual.
If errors occur suggesting hardware problems, you should contact
your hardware support group or field service.  It is a good idea to
examine the error log file regularly
(e.g. with the command \fItail \-r /var/log/messages\fP).
.Sh 2 "Filesystem checks, backups, and disaster recovery"
.PP
Periodically (say every week or so in the absence of any problems)
and always (usually automatically) after a crash,
all the filesystems should be checked for consistency
by
.Xr fsck (1).
The procedures of
.Xr reboot (8)
should be used to get the system to a state where a filesystem
check can be done manually or automatically.
.PP
Dumping of the filesystems should be done regularly,
since once the system is going it is easy to
become complacent.
Complete and incremental dumps are easily done with
.Xr dump (8).
You should arrange to do a towers-of-hanoi dump sequence; we tune
ours so that almost all files are dumped on two tapes and kept for at
least a week in most every case.  We take full dumps every month (and keep
these indefinitely).
Operators can execute ``dump w'' at login that will tell them what needs
to be dumped
(based on the
.Pn /etc/fstab
information).
Be sure to create a group
.B operator
in the file
.Pn /etc/group
so that dump can notify logged-in operators when it needs help.
.PP
More precisely, we have three sets of dump tapes: 10 daily tapes,
5 weekly sets of 2 tapes, and fresh sets of three tapes monthly.
We do daily dumps circularly on the daily tapes with sequence
`3 2 5 4 7 6 9 8 9 9 9 ...'.
Each weekly is a level 1 and the daily dump sequence level
restarts after each weekly dump.
Full dumps are level 0 and the daily sequence restarts after each full dump
also.
.PP
Thus a typical dump sequence would be:
.br
.ne 6
.TS
center;
c c c c c
n n n l l.
tape name	level number	date	opr	size
_
FULL	0	Nov 24, 1992	operator	137K
D1	3	Nov 28, 1992	operator	29K
D2	2	Nov 29, 1992	operator	34K
D3	5	Nov 30, 1992	operator	19K
D4	4	Dec 1, 1992	operator	22K
W1	1	Dec 2, 1992	operator	40K
D5	3	Dec 4, 1992	operator	15K
D6	2	Dec 5, 1992	operator	25K
D7	5	Dec 6, 1992	operator	15K
D8	4	Dec 7, 1992	operator	19K
W2	1	Dec 9, 1992	operator	118K
D9	3	Dec 11, 1992	operator	15K
D10	2	Dec 12, 1992	operator	26K
D1	5	Dec 15, 1992	operator	14K
W3	1	Dec 17, 1992	operator	71K
D2	3	Dec 18, 1992	operator	13K
FULL	0	Dec 22, 1992	operator	135K
.TE
We do weekly dumps often enough that daily dumps always fit on one tape.
.PP
Dumping of files by name is best done by
.Xr tar (1)
but the amount of data that can be moved in this way is limited
to a single tape.
Finally if there are enough drives entire
disks can be copied with
.Xr dd (1)
using the raw special files and an appropriate
blocking factor; the number of sectors per track is usually
a good value to use, consult
.Pn /etc/disktab .
.PP
It is desirable that full dumps of the root filesystem be
made regularly.
This is especially true when only one disk is available.
Then, if the
root filesystem is damaged by a hardware or software failure, you
can rebuild a workable disk doing a restore in the
same way that the initial root filesystem was created.
.PP
Exhaustion of user-file space is certain to occur
now and then; disk quotas may be imposed, or if you
prefer a less fascist approach, try using the programs
.Xr du (1),
.Xr df (1),
and
.Xr quot (8),
combined with threatening
messages of the day, and personal letters.
.Sh 2 "Moving filesystem data"
.PP
If you have the resources,
the best way to move a filesystem
is to dump it to a spare disk partition, or magtape, using
.Xr dump (8),
use
.Xr newfs (8)
to create the new filesystem,
and restore the filesystem using
.Xr restore (8).
Filesystems may also be moved by piping the output of
.Xr dump
to
.Xr restore .
The
.Xr restore
program uses an ``in-place'' algorithm that
allows filesystem dumps to be restored without concern for the
original size of the filesystem.  Further, portions of a
filesystem may be selectively restored using a method similar
to the tape archive program.
.PP
If you have to merge a filesystem into another, existing one,
the best bet is to use
.Xr tar (1).
If you must shrink a filesystem, the best bet is to dump
the original and restore it onto the new filesystem.
If you
are playing with the root filesystem and only have one drive,
the procedure is more complicated.
If the only drive is a Winchester disk, this procedure may not be used
without overwriting the existing root or another partition.
What you do is the following:
.IP 1.
GET A SECOND PACK, OR USE ANOTHER DISK DRIVE!!!!
.IP 2.
Dump the root filesystem to tape using
.Xr dump (8).
.IP 3.
Bring the system down.
.IP 4.
Mount the new pack in the correct disk drive, if
using removable media.
.IP 5.
Load the distribution tape and install the new
root filesystem as you did when first installing the system.
Boot normally
using the newly created disk filesystem.
.PP
Note that if you change the disk partition tables or add new disk
drivers they should also be added to the standalone system in
.Pn /sys/<architecture>/stand ,
and the default disk partition tables in
.Pn /etc/disktab
should be modified.
.Sh 2 "Monitoring system performance"
.PP
The
.Xr systat
program provided with the system is designed to be an aid to monitoring
systemwide activity.  The default ``pigs'' mode shows a dynamic ``ps''.
By running in the ``vmstat'' mode
when the system is active you can judge the system activity in several
dimensions: job distribution, virtual memory load, paging and swapping
activity, device interrupts, and disk and cpu utilization.
Ideally, there should be few blocked (b) jobs,
there should be little paging or swapping activity, there should
be available bandwidth on the disk devices (most single arms peak
out at 20-30 tps in practice), and the user cpu utilization (us) should
be high (above 50%).
.PP
If the system is busy, then the count of active jobs may be large,
and several of these jobs may often be blocked (b).  If the virtual
memory is active, then the paging demon will be running (sr will
be non-zero).  It is healthy for the paging demon to free pages when
the virtual memory gets active; it is triggered by the amount of free
memory dropping below a threshold and increases its pace as free memory
goes to zero.
.PP
If you run in the ``vmstat'' mode
when the system is busy, you can find
imbalances by noting abnormal job distributions.  If many
processes are blocked (b), then the disk subsystem
is overloaded or imbalanced.  If you have several non-dma
devices or open teletype lines that are ``ringing'', or user programs
that are doing high-speed non-buffered input/output, then the system
time may go high (60-70% or higher).
It is often possible to pin down the cause of high system time by
looking to see if there is excessive context switching (cs), interrupt
activity (in) and per-device interrupt counts,
or system call activity (sy).  Cumulatively on one of
our large machines we average about 60-200 context switches and interrupts
per second and about 50-500 system calls per second.
.PP
If the system is heavily loaded, or if you have little memory
for your load (2M is little in most any case), then the system
may be forced to swap.  This is likely to be accompanied by a noticeable
reduction in system performance and pregnant pauses when interactive
jobs such as editors swap out.
If you expect to be in a memory-poor environment
for an extended period you might consider administratively
limiting system load.
.Sh 2 "Recompiling and reinstalling system software"
.PP
It is easy to regenerate either the entire system or a single utility,
and it is a good idea to try rebuilding pieces of the system to build
confidence in the procedures.
.LP
In general, there are six well-known targets supported by