NAME

passwd − password file

DESCRIPTION

passwd contains for each user the following information:

login name
encrypted password
numerical user ID
numerical group ID
GCOS job number, box number, optional GCOS user ID
initial working directory
program to use as shell

This is an ASCII file.  Each field within each user’s entry is separated from the next by a colon.  The GCOS field is used only when communicating with that system, and in other installations can contain any desired information.  Each user is separated from the next by a new-line.  If the password field is null, no password is demanded; if the shell field is null, the shell itself is used. 

This file resides in directory /etc. Because of the encrypted passwords, it can and does have general read permission and can be used, for example, to map numerical user IDs to names. 

The encrypted password consists of 13 characters chosen from a 64-character alphabet (., /, 0−9, A−Z, a−z), except when the password is null, in which case the encrypted password is also null.  Password aging is effected for a particular user if his encrypted password in the password file is followed by a comma and a non-null string of characters from the above alphabet.  (Such a string must be introduced in the first instance by the super-user.) 

The first character of the age, M say, denotes the maximum number of weeks for which a password is valid. A user who attempts to login after his password has expired is forced to supply a new one. The next character, m say, denotes the minimum period in weeks which must expire before the password may be changed. The remaining characters define the week (counted from the beginning of 1970) when the password was last changed. (A null string is equivalent to zero.) M and m have numerical values in the range 0−63 that correspond to the 64-character alphabet shown above (i.e., / = 1 week; z = 63 weeks).  If m = M = 0 (derived from the string .  or ..) the user is forced to change his password the next time he logs in (and the “age” disappears from his entry in the password file).  If m > M (signified, e.g., by the string ./) only the super-user is able to change the password. 

FILES

/etc/passwd

SEE ALSO

getpwent(3C), group(4), login(1), passwd(1)

September 29, 2021