where these fields represent:
frank:yPf3M5qMgglUc:101:10:Frank G Fiamingo:/home/tardis/frank:/usr/bin/csh
The home directory, field 6 of /etc/passwd, specifies the location of the user's home within the operating system. The user is placed here by the login program. For a normal login user this directory should be owned by the user.
The shell, field 7 of /etc/passwd, is the program run when the user logs in. Generally this is a shell that acts as a command interpreter, reading from a terminal and translating the commands into system actions, e.g. sh (Bourne shell), csh (C shell), or tcsh (extended C shell). Occasionally this is not a shell, but a stand-alone program, as in the sysdiag passwd entry given above. Here when you login as "sysdiag" you go directly into the systems diagnostics program.
For SunOS 4.1.X you would generally edit the passwd file using the vipw command. This saves a copy of passwd as ptmp, uses the vi editor by default (or the editor set by your VISUAL or EDITOR environment variable), and verifies the consistency of the root entry before writing the file back to passwd. The shell for the root account must be listed in /etc/shells, if the file exists. The ptmp file also serves as a lock against a simultaneous use of vipw.