201 lines
4.9 KiB
Groff
201 lines
4.9 KiB
Groff
.TH PASSWD 5
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.SH NAME
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passwd, group, shadow \- user and group databases, shadow passwords
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.SH SYNOPSIS
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.B /etc/passwd
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.br
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.B /etc/group
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.br
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.B /etc/shadow
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.SH DESCRIPTION
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.B /etc/passwd
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lists all the users of the system, and
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.B /etc/group
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lists all the groups the users may belong to. Both files also contain
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encrypted passwords, numeric ID's etc. Encrypted passwords may be hidden
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in the file
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.B /etc/shadow
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if extra protection is warranted.
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.PP
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Each file is an text file containing one line per user or group. The data
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fields on a line are separated by colons. Each line in the password file
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has the following form:
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.PP
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.RS
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.I name:passwd:uid:gid:gecos:dir:shell
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.RE
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.PP
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The
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.I name
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field is the login name of a user, it is up to 8 letters or numbers long
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starting with a letter. The login name must be unique.
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The
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.I password
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field is either empty (no password), a 13 character encrypted password as
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returned by
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.BR crypt (3),
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or a login name preceded by two number signs (#) to index the shadow
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password file. Anything else (usually \(**) is invalid.
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The
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.I uid
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and
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.I gid
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fields are two numbers indicating the users user-id and group-id. These
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id's do not have to be unique, there may be more than one name with the same
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id's.
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The
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.I gecos
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field can be set by the user. It is expected to be a comma separated list
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of personal data where the first item is the full name of the user.
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The
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.I dir
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field
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is the path name of the users home directory.
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Lastly the
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.I shell
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field is the path name of the users login shell, it may be empty to indicate
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.BR /bin/sh .
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A MINIX 3 specific extension allows the shell field to contain extra space
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separated arguments for the shell.
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.PP
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Lines in the group file consist of four fields:
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.PP
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.RS
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.I name:passwd:gid:mem
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.RE
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.PP
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The
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.I name
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field is the name of the group, same restrictions as a login name.
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The
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.I passwd
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field may be used to let users change groups.
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The
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.I gid
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field is a number telling the group-id. The group-id is unique for a group.
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The
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.I mem
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field is a comma separated list of login names that are special members of
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the group. If a system supports supplementary group id's then a user's set
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of supplementary group id's is set to all the groups they are a member of.
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If a system allows one to change groups then one can change to a group one
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is a member of without using the group's password.
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.PP
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The shadow password file has precisely the same form as the password file,
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except that only the
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.I name
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or
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.I passwd
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fields are used as yet. The other fields are zero or empty. A password in
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the password file may have the form
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.BI "##" user
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to indicate the entry
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.I user
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in the shadow password file. The password in this entry is then used for
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authentication of the user. The shadow file can only be read by the
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privileged utility
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.BR pwdauth (8),
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so 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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.SS "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 reserved.
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The special password file entries are:
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.PP
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.RS
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.nf
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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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.fi
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.RE
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.PP
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The
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.B root
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id is of course the super user.
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The
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.B daemon
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id is used by some daemons. Some devices are protected so that only those
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daemons can access them.
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The
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.B bin
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id owns all sources and most binaries.
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The
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.BR uucp ,
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.BR news
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and
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.BR ftp
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id's are for serial line data transfer, usenet news, or ftp if so needed.
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The
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.B nobody
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id is used in those cases that a program may not have any privileges at all.
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The
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.B ast
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id is the honorary home directory for Andrew S. Tanenbaum, the creator of
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MINIX 3. You can also find the initial contents for a new home directory
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there.
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.PP
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The special group file entries are:
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.PP
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.RS
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.nf
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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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.fi
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.RE
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.PP
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Groups with the same name as special user id are used with those id's.
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The
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.B operator
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group is for the administrators of the system. Users in this group are
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granted special privileges.
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The
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.B other
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group is for ordinary users.
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The
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.B tty
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group is for terminal devices, and associated set-gid commands.
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Same thing with the
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.B kmem
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group and memory devices.
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.SH FILES
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.TP 15n
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.B /etc/passwd
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The user database.
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.TP
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.B /etc/group
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The group database.
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.TP
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.B /etc/shadow
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The shadow password file.
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.SH "SEE ALSO"
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.BR login (1),
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.BR passwd (1),
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.BR su (1),
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.BR crypt (3),
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.BR getpwent (3),
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.BR getgrent (3),
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.BR pwdauth (8).
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.SH NOTES
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The
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.B nobody
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and
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.B nogroup
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id's are likely to be renumbered to the highest possible id's once it is
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figured out what they are.
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.SH AUTHOR
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Kees J. Bot (kjb@cs.vu.nl)
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