Solaris 2.x/SunOS 5.x System Administration Files and their purpose.

File                    Purpose
----                    -------
/kernel/unix            This is the kernel; it controls basic operating system 
services.
/etc/system             This allows access for setting kernel parameters.
/ufsboot 
/usr/lib/fs/ufs         This is the boot block used for booting the kernel.
/etc/passwd             
/etc/shadow             User login, password and password aging information.
/etc/group              User groups account information.
/etc/hosts              Local host and IP address information.
/etc/aliases            Electronic mail addresses, aliases and groups.
/etc/motd               Message of the day. 
/etc/defaultdomain      Domain name the system uses.
/etc/hostname.XX0       Hostname on the primary ethernet.
/etc/hoxtname.??1       Hostname on the secondary ethernet.
/etc/ethers             Ethernet address and hostname (jumpstart server).
/etc/bootparams         Defines root/swap for diskless clients (jumpstart).
/tftpboot/inetboot      Boot for clients.
/etc/inittab            Read by init to control switching between run levels.
/sbin/rcS               Script to boot to single user mode
/sbin/rcX(X=1,2,3)      Scripts init uses for changing run levels.
/etc/init.d             Directory containing startup scripts.
/etc/saf                Directory of tty port monitors.
/etc/ttydefs            Terminal line settings information for ttymon.
/usr/share/lib/terminfo Terminal capability database.
/etc/services           Internet services and ports.
/etc/rpc                Library routines for remote procedure calls.
/etc/protocols          Network protocol name database.
/etc/networks           Network name and address database.
/etc/netmasks           Network mask database.
/etc/inetd.conf         Internet servers database.
/etc/defaultrouter      Defines the default router.
/etc/nsswitch.conf      Configuration file for the name service.
/etc/netconfig          Network configuration database.
/etc/lp                 Directory of printer setup files.
/etc/gateways           Network/host destinations routing used by routed.
/etc/vfstab             Table of filesystem mount points.
/etc/mnttab             List of current mount points.
/etc/dfs/shares         Shared filesystems accessable from other systems.
/etc/rmtab              List of remote mount points.
/etc/dfs/fstypes        List distributed file system types.
/etc/default/fs         Local filesystem type.
/etc/default/login      Policy for default logins.
/etc/default/passwd     Policy for passwd requirements.
/etc/default/su         Sets the file used to log all su attempts.
/etc/default/cron       Sets the file used to log cron information.
/etc/default/tar        Defines default device of tar.
/var/sadm/install       Directory containing install information.
/etc/profile            System wide sh/ksh environment settings file.
/etc/.login             System wide csh environment settings file.
/reconfigure            Upon reboot triggers reconfiguration of devices.
/AUTOINSTALL            Upon reboot triggers autoinstall/jumpstart.