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Unix System Administration. Chapter 31. Daemons. Out of the Goo, the Primordial Process. Init ... all user processes and all but a few system processes. Configured ...

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  1. Unix System Administration Chapter 31 Daemons

  2. Out of the Goo, the Primordial Process • Init • Always the first process to run after system boot • Always PID 1 • Ancestor of all user processes and all but a few system processes • Configured using /etc/inittab • Exorcises undead zombie process • If init dies, the system will hang or reboot

  3. It’s a Bird, It’s a Plane,No It’s the Super Daemon • Inetd • Daemon that manages other daemons • The daemons it manages must be programmed to be started and managed by inetd • Uses /etc/inetd.conf and /etc/services as configuration files • Simple daemons (echo, discard, etc) are built-into inetd • You need to send SIGHUP to inetd after editing /etc/inetd.conf to tell it to reread the file

  4. /etc/inetd.conf (abridged) # Syntax for socket-based Internet services: # <service_name> <socket_type> <proto> <flags> <user> # <server_pathname> <args> # ftp stream tcp nowait root /usr/sbin/in.ftpd in.ftpd telnet stream tcp nowait root /usr/sbin/in.telnetd in.telnetd echo stream tcp nowait root internal echo dgram udp wait root internal talk dgram udp wait root /usr/sbin/in.talkd in.talkd

  5. /etc/services (abridged) echo 7/tcp echo 7/udp ftp-data 20/tcp ftp 21/tcp telnet 23/tcp talk 517/udp

  6. Mapping Those Pesky Ports • Portmap (aka Rpcbind) • Runs on port 111 • Maps between RPC service numbers and TCP/IP port numbers • RPC services register their service number, version and port number with portmap/rpcbind when the start up • Clients contact portmap/rpcbind to find the port that a particular service is running on. • Use rpcinfo -p to display registered services

  7. Let’s Wrap It Up! • TCP_Wrappers • Used to provide IP address-level security to daemons run from inetd • Can also be used with non-inetd daemons if they can link with the libwrap library • Logs successful and failed attempts via syslog facility • Requires modification to /etc/inetd.conf • Written by Wietse Venema of the Netherlands • ftp://ftp.porcupine.org/pub/security/index.html

  8. TCP_Wrapperized /etc/inetd.conf # Syntax for socket-based Internet services: # <service_name> <socket_type> <proto> <flags> <user> # <server_pathname> <args> # ftp stream tcp nowait root /usr/sbin/tcpd in.ftpd telnet stream tcp nowait root /usr/sbin/tcpd in.telnetd echo stream tcp nowait root internal echo dgram udp wait root internal talk dgram udp wait root /usr/sbin/tcpd in.talkd

  9. /etc/hosts.allow & /etc/hosts.deny /etc/hosts.allow ALL: localhost,krusty in.telnetd: beast,bugs in.rlogind: beast,bugs in.rexecd: beast,bugs,159.91. in.rshd: beast,bugs in.fingerd: ALL in.talkd: ALL /etc/hosts.deny ALL: ALL

  10. Daemons Daemons Everywhere ... • nfsd, rpc.lockd & rpc.statd - file sharing • ypbind, ypserv, ypxfrd - NIS daemons • comsat - e-mail notification • talkd - chat server • routed, gated - routing • innd, nntpd - Network News • syslogd - logging server • httpd - web server

  11. … Even in Your Underwear • Ftpd - file transfer • telnetd - remote terminal • rshd, rexec - remote shell • rlogin - remote login • xntp - time sync • dhcpd, bootpd, rarpd - IP address servers • popper, ipopd, imapd - e-mail servers • sendmail - e-mail routing server

  12. Exorcise These Daemons! • Besides a Unix service, what is a “daemon?” • What happens if inetd dies? • What is the name of the TCP_wrapper daemon?

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