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Another version of this page is provided by the shadow-utils project
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passwd(5) File Formats Manual passwd(5)
passwd - password file
The /etc/passwd file is a text file that describes user login
accounts for the system. It should have read permission allowed
for all users (many utilities, like ls(1) use it to map user IDs
to usernames), but write access only for the superuser.
In the good old days there was no great problem with this general
read permission. Everybody could read the encrypted passwords,
but the hardware was too slow to crack a well-chosen password,
and moreover the basic assumption used to be that of a friendly
user-community. These days many people run some version of the
shadow password suite, where /etc/passwd has an 'x' character in
the password field, and the encrypted passwords are in
/etc/shadow, which is readable by the superuser only.
If the encrypted password, whether in /etc/passwd or in
/etc/shadow, is an empty string, login is allowed without even
asking for a password. Note that this functionality may be
intentionally disabled in applications, or configurable (for
example using the "nullok" or "nonull" arguments to pam_unix(8)).
If the encrypted password in /etc/passwd is "*NP*" (without the
quotes), the shadow record should be obtained from an NIS+
server.
Regardless of whether shadow passwords are used, many system
administrators use an asterisk (*) in the encrypted password
field to make sure that this user can not authenticate themself
using a password. (But see NOTES below.)
If you create a new login, first put an asterisk (*) in the
password field, then use passwd(1) to set it.
Each line of the file describes a single user, and contains seven
colon-separated fields:
name:password:UID:GID:GECOS:directory:shell
The field are as follows:
name This is the user's login name. It should not contain
capital letters.
password
This is either the encrypted user password, an asterisk
(*), or the letter 'x'. (See pwconv(8) for an explanation
of 'x'.)
UID The privileged root login account (superuser) has the user
ID 0.
GID This is the numeric primary group ID for this user.
(Additional groups for the user are defined in the system
group file; see group(5)).
GECOS This field (sometimes called the "comment field") is
optional and used only for informational purposes.
Usually, it contains the full username. Some programs
(for example, finger(1)) display information from this
field.
GECOS stands for "General Electric Comprehensive Operating
System", which was renamed to GCOS when GE's large systems
division was sold to Honeywell. Dennis Ritchie has
reported: "Sometimes we sent printer output or batch jobs
to the GCOS machine. The gcos field in the password file
was a place to stash the information for the $IDENTcard.
Not elegant."
directory
This is the user's home directory: the initial directory
where the user is placed after logging in. The value in
this field is used to set the HOME environment variable.
shell This is the program to run at login (if empty, use
/bin/sh). If set to a nonexistent executable, the user
will be unable to login through login(1). The value in
this field is used to set the SHELL environment variable.
/etc/passwd
If you want to create user groups, there must be an entry in
/etc/group, or no group will exist.
If the encrypted password is set to an asterisk (*), the user
will be unable to login using login(1), but may still login using
rlogin(1), run existing processes and initiate new ones through
rsh(1), cron(8), at(1), or mail filters, etc. Trying to lock an
account by simply changing the shell field yields the same result
and additionally allows the use of su(1).
chfn(1), chsh(1), login(1), passwd(1), su(1), crypt(3),
getpwent(3), getpwnam(3), group(5), shadow(5), vipw(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 passwd(5)
Pages that refer to this page: chage(1), chfn(1), chfn(1@@shadow-utils), chsh(1), chsh(1@@shadow-utils), expiry(1), indomcachectl(1), login(1), login(1@@shadow-utils), lslogins(1), passwd(1), systemd-firstboot(1), crypt(3), fgetpwent(3), getgrouplist(3), getpw(3), getpwent(3), getpwent_r(3), getpwnam(3), sysexits.h(3head), ftpusers(5), group(5), login.defs(5), shadow(5), slapd.backends(5), slapd-passwd(5), systemd.exec(5), credentials(7), environ(7), grpck(8), newusers(8), nologin(8), nscd(8), pwck(8), vipw(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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