Daemons

Ying ZhangCMSC691X, Summer02

Outline

Introduction Init and Cron System daemons Print daemons and NFS daemons Time synchronization daemons Booting and configuration daemons Internet daemons Inetd

Introduction

Daemon A background process that performs a

specific function or system-related task Independent of kernel

Init

The primordial process PID 1 Place the system in single-user

mode or spawns a shell to read the systems’ startup scripts.

Define several “run levels” that determine what set of system resources should be enabled

Cron

Schedule commands Mainly used for administrative

purposes Management of accounting and log files Daily cleanup of the file system Backup of the file system

System daemons

The paging daemon Part of the virtual memory system Update the page into memory from the swap area

in the case of page faults Write out pages to the swap device and update

page table if no physical pages are available Pageout, vhand, kpiod, pagedaemon

The swapping daemon Monitor the number of page faults that occur in

proportion to the number of memory reference Move process out to swap space to avoid

“thrashing” if too many faults occur Swapper, kswapd

System daemons (cont.)

The filesystem synchronization daemon Execute sync system call every 30

seconds Cause all “dirty” block to be written out

Update, syncer, fsflush

Printing daemons and NFS daemons

Printing daemons Provide printing-related service

NFS daemons nfsd:

Run on file servers and handle requests from NFS client

mountd Accept filesystem mount requests from potential

NFS client amd and automount lockd and statd biod

Time synchronization daemon

Timed One or more machines are designated as time

masters Their clocks are considered authoritative

Other machines are slave Periodically converse with a master to learn

the time and then adjust their internal clock

Xntpd Implement Network Time Protocol in RFC1119 Servers are arranged in a hierarchal tree

Booting and configuration daemons

bootp Boot server

tftpd Trivial file transfer server

rarpd Map Ethernet address to IP address

bootparamd Use /etc/bootparams to tell diskless clients where

to find their filesystems dhcpd

Dynamic address assignment

Internet daemons

talkd: network chat service comsat: notify users of new email sendmail: transport electronic mail snmpd: provide remote network

management service rwhod: maintain remote user list ftpd: file transfer server poper: basic mailbox server

Internet daemons (cont.)

imapd: deluxe mailbox server rlogind: remote login server telnetd: another remote login server sshd: secure remote login server rshd: remote command execution server rexecd: another command execution

server rpc.exd: a third command execution

server routed and gated

Internet daemons (cont.)

named: DNS server syslogd: process log message fingerd: look up users httpd: WWW server

inetd Overview

It is a daemon that manages other daemons It attaches itself to network ports and starts up the

appropriate daemon when a connection occurs. Configuring inetd

inetd consults a config file to determine which network ports it should listen to

/etc/inetd.conf

Service Name

Type of socket

Protocol MultipleRequest

username Full qualified name and argument

ftp stream tcp nowait root /usr/sbin/ftpd ftpd

mountd/1 dgram rpc/udp wait root /usr/sbin/mountd mountd

inetd (cont.)

The services file Map service numbers to port numbers /etc/services

inetd (cont.)

Restarting inetd Have inetd to reread /etc/inetd.conf to put the

modification of this file into effect Send inetd a hangup signal

Securing inetd Enable only the services that you absolutely

need and turn everything else off Portmap/rpcbind

Map RPC services to TCP and UDP port

Q?

Questions?