178 lines
6.0 KiB
Groff
178 lines
6.0 KiB
Groff
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PASSWD(5) Minix Programmer's Manual PASSWD(5)
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NAME
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passwd, group, shadow - user and group databases, shadow passwords
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SYNOPSIS
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/etc/passwd
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/etc/group
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/etc/shadow
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DESCRIPTION
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/etc/passwd lists all the users of the system, and /etc/group lists all
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the groups the users may belong to. Both files also contain encrypted
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passwords, numeric ID's etc. Encrypted passwords may be hidden in the
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file /etc/shadow if extra protection is warranted.
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Each file is an text file containing one line per user or group. The
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data fields on a line are separated by colons. Each line in the password
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file has the following form:
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name:passwd:uid:gid:gecos:dir:shell
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The name field is the login name of a user, it is up to 8 letters or
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numbers long starting with a letter. The login name must be unique. The
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password field is either empty (no password), a 13 character encrypted
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password as returned by crypt(3), or a login name preceded by two number
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signs (#) to index the shadow password file. Anything else (usually *)
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is invalid. The uid and gid fields are two numbers indicating the users
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user-id and group-id. These id's do not have to be unique, there may be
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more than one name with the same id's. The gecos field can be set by the
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user. It is expected to be a comma separated list of personal data where
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the first item is the full name of the user. The dir field is the path
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name of the users home directory. Lastly the shell field is the path
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name of the users login shell, it may be empty to indicate /bin/sh. A
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Minix specific extension allows the shell field to contain extra space
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separated arguments for the shell.
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Lines in the group file consist of four fields:
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name:passwd:gid:mem
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The name field is the name of the group, same restrictions as a login
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name. The passwd field may be used to let users change groups. The gid
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field is a number telling the group-id. The group-id is unique for a
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group. The mem field is a comma separated list of login names that are
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special members of the group. If a system supports supplementary group
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id's then a user's set of supplementary group id's is set to all the
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groups they are a member of. If a system allows one to change groups
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then one can change to a group one is a member of without using the
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group's password.
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1
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PASSWD(5) Minix Programmer's Manual PASSWD(5)
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The shadow password file has precisely the same form as the password
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file, except that only the name or passwd fields are used as yet. The
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other fields are zero or empty. A password in the password file may have
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the form ##user to indicate the entry user in the shadow password file.
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The password in this entry is then used for authentication of the user.
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The shadow file can only be read by the privileged utility pwdauth(8), so
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that the encrypted passwords in the shadow file are kept secret, and thus
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safe from a dictionary attack.
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Special password and group file entries
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There are several entries in the password and group files that are
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preallocated for current or future use. All id's less than 10 are
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reserved. The special password file entries are:
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root:##root:0:0:Big Brother:/usr/src:
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daemon:*:1:1:The Deuce:/etc:
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bin:##root:2:0:Binaries:/usr/src:
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uucp:*:5:5:UNIX to UNIX copy:/usr/spool/uucp:/usr/sbin/uucico
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news:*:6:6:Usenet news:/usr/spool/news:
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ftp:*:7:7:Anonymous FTP:/usr/ftp:
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nobody:*:9999:99::/tmp:
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ast:*:8:3:Andrew S. Tanenbaum:/usr/ast:
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The root id is of course the super user. The daemon id is used by some
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daemons. Some devices are protected so that only those daemons can
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access them. The bin id owns all sources and most binaries. The uucp,
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news and ftp id's are for serial line data transfer, usenet news, or ftp
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if so needed. The nobody id is used in those cases that a program may
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not have any privileges at all. The ast id is the honorary home
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directory for Andrew S. Tanenbaum, the creator of Minix. You can also
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find the initial contents for a new home directory there.
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The special group file entries are:
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operator:*:0:
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daemon:*:1:
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bin:*:2:
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other:*:3:
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tty:*:4:
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uucp:*:5:
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news:*:6:
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ftp:*:7:
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kmem:*:8:
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nogroup:*:99:
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Groups with the same name as special user id are used with those id's.
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The operator group is for the administrators of the system. Users in
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this group are granted special privileges. The other group is for
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ordinary users. The tty group is for terminal devices, and associated
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set-gid commands. Same thing with the kmem group and memory devices.
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2
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PASSWD(5) Minix Programmer's Manual PASSWD(5)
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FILES
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/etc/passwd The user database.
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/etc/group The group database.
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/etc/shadow The shadow password file.
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SEE ALSO
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login(1), passwd(1), su(1), crypt(3), getpwent(3), getgrent(3),
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pwdauth(8).
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NOTES
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The nobody and nogroup id's are likely to be renumbered to the highest
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possible id's once it is figured out what they are.
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AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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3
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