1. Daemons Ying Zhang CMSC691X, Summer02

2. Outline  Introduction  Init and Cron  System daemons  Print daemons and NFS daemons  Time synchronization daemons  Booting and configuration daemons  Internet daemons  Inetd

3. Introduction  Daemon A background process that performs a specific function or system-related task Independent of kernel

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Internet daemons (cont.)  named: DNS server  syslogd: process log message  fingerd: look up users  httpd: WWW server

14. 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 ProtocolMultiple Request usernameFull qualified name and argument ftpstreamtcpnowaitroot/usr/sbin/ftpd ftpd mountd/1dgramrpc/udpwaitroot/usr/sbin/mountd mountd

15. inetd (cont.)  The services file Map service numbers to port numbers /etc/services

16. 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

17. Q? Questions?