Unix System Administration Chapter 31 Daemons

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

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

/etc/inetd.conf (abridged) # Syntax for socket-based Internet services: # 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

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

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

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

TCP_Wrapperized /etc/inetd.conf # Syntax for socket-based Internet services: # 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

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

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

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

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