Daemons

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. 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 inetd

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?