|
Devices appear
as files in the directory /dev. They can be read, or written to,
if you have the permission to do so. The listing of the file reveals some
important details about the device, for example:
ls -l
/dev/ttyS3
on my system
produces the following output:
crwxr-xr-x
1 root tty
4, 67 Mar 13 22:59 ttyS3
The initial
"c" indicates a character device. "b" would mean "block device", "p"=FIFO
device, "u"=unbuffered character device, "d"=directory, "l"=symbolic link.
The numbers "4, 67" mean that the device major number is 4 and the minor
number is 67. To make some devices usable to all users on your system,
you may need to set the proper permissions. For example:
ls -l /dev/usb/scanner0
chmod 666 /dev/usb/scanner0
Here is a
list of some common devices:
/dev/ttyS0
- the first serial port. The mouse is typically connected here.
/dev/ttyS1 - the second serial port. This may well be the device
to which your modem is connected.
/dev/ttyS2 and /dev/ttyS3 the third and fourth
serial port (typically not present, but your internal modem may well be
configured as one of these).
/dev/modem - the serial modem. In the typical case, a symbolic
link to /dev/ttyS1, /dev/ttyS2, /dev/ttyS3 or /dev/ttyS0, depending to
which serial port your modem is connected.
/dev/mouse - mouse. In the typical case, a symbolic link to /dev/ttyS0
or similar (see above), depending to which serial port your mouse is connected.
/dev/lp0 - printer on the first parallel port. That's where
normally printers are connected.
/dev/lp1 - printer on the second parallel port (typically
not present).
/dev/fd0 - first floppy disk drive (almost always present).
/dev/fd0H1440 - driver for the first floppy drive in the high-density
mode (1440 kB). Generally, this (or a driver with a device with a similar
descriptive name) is invoked when formatting a floppy drive to a particular
density. Slackware also comes with drivers that allow for formatting a
3.5" diskette with up to 1.7MB of space. Red Hat and Mandrake do not contain
these device drivers files by default.
/dev/fd1 - second floppy disk drive.
/dev/hda - first IDE hard drive (whole drive). Most hard
drives on IBM-compatibile PCs are IDE.
/dev/hdb - second IDE hard drive (whole drive). On many computers,
the IDE cdrom drive is attached here.
/dev/hdc - third IDE drive (whole drive). On many computers,
the IDE cdrom drive is attached here.
/dev/cdrom - a symbolic link to the appropriate drive interface,
typically /dev/hdc or /dev/hdb (a CDROM) or /dev/scd0 (a CD-R/RW
writer).
/dev/hda1 - the first partition on the first IDE hard drive.
/dev/hda2 is the second partion on the first IDE hard drive. As one could
guess, /dev/hdd8 would be the eight partition on the fourth IDE hard drive.
/dev/tty1 - the first text console. /dev/tty2 is
the second text console, etc.
/dev/dsp - digital audio, i.e., the sound card. "dsp" stands
for "digital signal processing".
/dev/sndstat - do cat /dev/sndstat to learn about the
status of your sound devices.
/dev/null - used when you want to send output into oblivion.
/dev/random - used to read pseudo-random numbers. Do cat
/dev/random to display garbage-looking characters on your screen.
There is also /dev/urandom to generate lower-quality random sequences.
/dev/sda -the first SCSI drive (whole drive). On a home machine,
you are unlikely to have any SCSI drives (expensive).
/dev/sdb - the second scsi drive ("sdc" is the third scsi drive,
etc. There can be many scsi drive on a system).
/dev/sda1 - the first partition on the first scsi drive.
/dev/sr0 - the first scsi CD drive (sometimes called /dev/scd0).
If you have an ATAPI CD writer, it will also be likely here.
/dev/sr1-is the second scsi CD drive (sometimes called /dev/scd1),
(/dev/sr2 is the third scsi CD drive, etc. There can be many
scsi CD drives on the system).
/dev/usb/scanner0 - a usb scanner. Try: less /usr/src/linux/Documentation/usb/scanner.txt
for an info on scanner configuration from scratch.
For more
info try:
less /usr/src/linux/Documentation/devices.txt
man MAKEDEV
As explained
in /usr/src/linux/Documentation/devices.txt, I may need to create some
symbolic links to device files locally to configure my system. This is
merely a tabulation of existing practice, and does not constitute a recommendation.
However, if the links exist, they should have the following uses:
/dev/mouse
Current mouse port***
/dev/tape Current tape device
/dev/cdrom Current CD-ROM device***
/dev/cdwriter Current CD-writer device (but my RedHat
have /dev/cdrecorder)
/dev/scanner Current scanner device
/dev/modem Current dialout (modem) port***
/dev/root Current root filesystem
/dev/swap Current swap device
The *** mark
the symbolic links that are surely present on my Mandrake system.
For example, if having problems with mouse I would do something like (as
root):
ls -l /dev/mouse
[see if the mouse device is present and where it points]
ln -s /dev/ttyS0 /dev/mouse
[create a symbolic link so that /dev/mouse point to the first serial port]
For SCSI
(and ATAPI) devices, /dev/tape and /dev/cdrom should point to the ``cooked''
devices (/dev/st* and /dev/sr*, respectively), whereas /dev/cdwriter and
/dev/scanner should point to the appropriate generic SCSI devices (/dev/sg*).
Non-transient
sockets and named pipes may exist in /dev. Common entries are:
/dev/printer socket lpd
local socket
/dev/log socket
syslog local socket
/dev/gpmdata socket gpm
mouse multiplexer
Some Linux
daemons
Daemons are
"resident"programs that periodically wake up, check your system and may
perform certain functions. They do not take any input and don't normally
produce any output. Your Linux system is likely set to run quite a number
of daemons. Most of them can be (dis)selected by running the program ntsysv
(RedHat) as root and checking the appropriate box. The short description
of each daemon is available under netsysv by pressing .
If the daemon you need is not listed in ntsysv, you need to insert
your RedHat/Mandrake installation CD and install the appropriate package.
The alternative to ntsysv may be tksysv (type as root,
in X terminal), which is perhaps more flexible, but way more complicated
(it lets you set up the list of daemons to run in each runlevel). Another,
simpler and even more powerful+flexible+difficult-to-use tool is /sbin/chkconfig.
Here is a
short list of popular daemons with a brief description:
anacron
- checks 'cron' jobs that were left out due to down time and executes
them. Useful if you have cron jobs scheduled but don't run your machine
all the time--anacron will detect that during bootup.
amd - automount daemon (automatically mounts removable media).
apmd - Advanced Power Management BIOS daemon. For use on machines,
especially laptops, that support apm.
arpwatch - keeps watch for ethernet/ip address pairings.
atd - runs jobs queued by the "at" command.
autofs - control the operation of automount daemons (competition
to amd).
bootparamd - server process that provides information to diskless
clients necessary for booting.
crond - automatic task scheduler. Manages the execution of tasks
that are executed at regular but infrequent intervals, such as rotating
log files, cleaning up /tmp directories, etc.
cupsd - the Common UNIX Printing System (CUPS) daemon. CUPS is
an advanced printer spooling system which allows setting of printer options
and automatic availability of a printer configured on one server in the
whole network. The default printing system of Linux Mandrake.
dhcpd - implements the Dynamic Host Configuration Protocol (DHCP)
and the Internet Bootstrap Protocol (BOOTP).
gated - routing daemon that handles multiple routing protocols
and replaces routed and egpup.
gpm - useful mouse server for applications running on the Linux
text console.
httpd - daemon for the Apache webserver.
inetd - listens for service requests on network connections,
particularly dial-in services. This daemon can automatically load and
unload other daemons (ftpd, telnetd, etc.), thereby economizing on system
resources. Newer systems use xinetd instead.
isdn4linux - for users of ISDN cards.
kerneld - automatically loads and unloads kernel modules.
klogd - the daemon that intercepts and displays/logs the kernel
messages depending on the priority level of the messages. The priority
is (copied from /usr/include/linux/kernel.h ):
KERN_EMERG "<0>" system
is unusable
KERN_ALERT "<1>" action
must be taken immediately
KERN_CRIT "<2>" critical
conditions
KERN_ERR "<3>"
error conditions
KERN_WARNING "<4>" warning condition
KERN_NOTICE "<5>" normal but significant
condition
KERN_INFO "<6>" informational
KERN_DEBUG "<7>" debug-level
messages
The messages typically go to the appropriately named files in the directory
/var/log/kernel.
kudzu
- detects and configures new or changed hardware during boot.
keytable - loads selected keyboard map.
linuxconf - the linuxconf configuration tool. The automated part
is run if you want linuxconf to perform various tasks at boottime to maintain
the system configuration.
lpd - printing daemon.
mcserv - server program for the Midnight Commander networking
file system. It provides access to the host file system to clients running
the Midnight file system (currently, only the Midnight Commander file
manager). If the program is run as root the program will try to get a
reserved port otherwise it will use 9876 as the port. If the system has
a portmapper running, then the port will be registered with the portmapper
and thus clients will automatically connect to the right port. If the
system does not have a portmapper, then a port should be manually specified
with the -p option (see below).
named - the Internet Domain Name Server (DNS) daemon.
netfs - network filesystem mounter. Used for mounting nfs, smb
and ncp shares on boot.
network -activates all network interfaces at boot time by calling
scripts in /etc/sysconfig/network-scripts .
nfsd - used for exporting nfs shares when requested by remote
systems.
nfslock - starts and stops nfs file locking service.
numlock - locks numlock key at init runlevel change.
pcmcia - generic services for pcmcia cards in laptops.
portmap - needed for Remote Procedure Calls. Most likely, you
need it for running network.
postfix - mail transport agent which is a replacement for sendmail.
Now the default on desktop installations of Mandrake (RedHat uses sendmail
instead).
random - saves and restores the "entropy" pool for higher quality
random number generation.
routed - daemon that manages routing tables.
rstatd - kernel statistics server.
rusersd, rwalld - identification of users and "wall"
messaging services for remote users.
rwhod - server which maintains the database used by the rwho(1)
and ruptime(1) programs. Its operation depends on the ability to broadcast
messages on a network.
sendmail - mail transfer agent. This is the agent that comes
with Red Hat.
smbd - the SAMBA (or smb) daemon, a network connectivity
services to MS Windows computers on your network (hard drive sharing,
printers, etc).
squid - An http proxy with caching. Proxies relay requests from
clients to the outside world, and return the results. You would use this
particular proxy if you wanted to use your linux computer as a gateway
to the Internet for other computer on your network. Another (and probably
safer at home) way to do it, is to set up masquarading.
syslogd - manages system activity logging. The configuration
file is /etc/syslog.conf .
smtpd - Simple Mail Transfer Protocol, designed for the exchange
of electronic mail messages. Several daemons that support SMTP are available,
including sendmail, smtpd, rsmtpd, qmail, zmail, etc.
usb - daemon for devices on Universal Serial Bus.
xfs - X font server.
xntpd - finds the server for a NIS domain and stores the information
about it in a binding file.
ypbind - NIS binder. Needed if computer is part of Network Information
Service domain.
Next > Part
4.5: Networking
|
| 