mirror of https://github.com/mkerrisk/man-pages
128 lines
4.3 KiB
Groff
128 lines
4.3 KiB
Groff
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.\" Copyright (c) 1993 Michael Haardt (michael@moria.de), Fri Apr 2 11:32:09 MET DST 1993
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.\"
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, write to the Free
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.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
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.\" USA.
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.\"
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.\" Modified Sun Jul 25 10:46:28 1993 by Rik Faith (faith@cs.unc.edu)
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.\" Modified Sun Aug 21 18:12:27 1994 by Rik Faith (faith@cs.unc.edu)
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.\" Modified Sun Jun 18 01:53:57 1995 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Mon Jan 5 20:24:40 MET 1998 by Michael Haardt
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.\" (michael@cantor.informatik.rwth-aachen.de)
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.TH PASSWD 5 1998-01-05 "File formats" "Linux Programmer's Manual"
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.SH NAME
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passwd \- password file
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.SH DESCRIPTION
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.B Passwd
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is a text file, that contains a list of the system's accounts,
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giving for each account some useful information like user ID,
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group ID, home directory, shell, etc.
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Often, it also contains the encrypted passwords for each account.
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It should have general read permission (many utilities, like
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.BR ls (1)
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use it to map user IDs to user names), but write access only for the
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superuser.
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.PP
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In the good old days there was no great problem with this general
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read permission. Everybody could read the encrypted passwords, but the
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hardware was too slow to crack a well-chosen password, and moreover, the
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basic assumption used to be that of a friendly user-community. These days
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many people run some version of the shadow password suite, where
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.I /etc/passwd
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has *'s instead of encrypted passwords, and the encrypted passwords are in
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.I /etc/shadow
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which is readable by the superuser only.
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.PP
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Regardless of whether shadow passwords are used, many sysadmins
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use a star in the encrypted password field to make sure
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that this user can not authenticate him- or herself using a
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password. (But see the Notes below.)
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.PP
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If you create a new login, first put a star in the password field,
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then use
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.BR passwd (1)
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to set it.
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.PP
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There is one entry per line, and each line has the format:
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.sp
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.RS
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account:password:UID:GID:GECOS:directory:shell
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.RE
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.sp
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The field descriptions are:
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.sp
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.RS
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.TP 1.0in
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.I account
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the name of the user on the system. It should not contain capital letters.
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.TP
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.I password
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the encrypted user password or a star.
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.TP
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.I UID
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the numerical user ID.
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.TP
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.I GID
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the numerical primary group ID for this user.
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.TP
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.I GECOS
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This field is optional and only used for informational purposes.
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Usually, it contains the full user name. GECOS means General Electric
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Comprehensive Operating System, which has been renamed to GCOS when
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GE's large systems division was sold to Honeywell. Dennis Ritchie has
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reported: "Sometimes we sent printer output or batch jobs to the GCOS
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machine. The gcos field in the password file was a place to stash the
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information for the $IDENTcard. Not elegant."
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.TP
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.I directory
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the user's $HOME directory.
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.TP
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.I shell
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the program to run at login (if empty, use
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.BR /bin/sh ).
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If set to a non-existing executable, the user will be unable to login
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through
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.BR login (1).
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.RE
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.SH NOTE
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If you want to create
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user groups, their GIDs must be equal and there must be an entry in
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\fI/etc/group\fP, or no group will exist.
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.PP
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If the encrypted password is set to a star, the user will be unable
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to login using
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.BR login (1),
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but may still login using
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.BR rlogin (1),
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run existing processes and initiate new ones through
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.BR rsh (1),
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.BR cron (1),
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.BR at (1),
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or mail filters, etc. Trying to lock an account by simply changing the
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shell field yields the same result and additionally allows the use of
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.BR su (1).
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.SH FILES
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.I /etc/passwd
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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 group (5),
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.BR shadow (5)
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