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Understanding /etc/passwd file format

Posted by Vivek Gite [Last updated: February 22, 2006]

It stores essential information required during login i.e. user account information.

It contains one entry per line for each user (or user account) of the system. All fields are separated by a colon (:) symbol. Total seven fields as follows.

Generally, passwd file entry looks as follows (click to enlarge image):

  1. Username: It is used when user logs in. It should be between 1 and 32 characters in length.
  2. Password: An x character indicates that encrypted password is stored in /etc/shadow file.
  3. User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
  4. Group ID (GID): The primary group ID (stored in /etc/group file)
  5. User ID Info: The comment field. It allow you to add extra information about the users such as user's full name, phone number etc. This field use by finger command.
  6. Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
  7. Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please not it does not have to be a shell.

Caution: The permission on the /etc/passwd file should be read only to users (rw-r—r--) and the owner must be root:

$ ls -l /etc/passwd

Output:

-rw-r--r--  1 root root 1941 Oct 13 02:08 /etc/passwd

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Discussion on This FAQ

  1. Ruwan.gawarammana Says:

    What are the differences between system calls and Library functions?

  2. surya Says:

    What is the need for /etc/shadow file, when there is /etc/shadow file?

    Can the password be maintained in /etc/paswd file itself?

    please tell me why Developers implemented two files /etc/passwd and /etc/shadow/

  3. Gabe Says:

    surya - There may be other reasons, but one reason is that the /etc/shadow file is not readable by any user except root. Whereas the /etc/passwd has legitimate reasons to be read by other users. Even though the passwords can be encrypted directly in /etc/passwd, that is still less secure than have even the encrypted passwords hidden.

  4. Bill Says:

    I have been asked to create a new user on an HP-UX 7.05 machine circa 1990.

    Editing the /etc/admin file in Motif to add my user account resulted in that user having denied access. the user name was as added as a user to /etc/groups. I used a new UID fot the user.

    Any clues as to what i did wrong?

    Thanks

  5. Bill Says:

    That was /etc/passwd

  6. Praveen Says:

    First let me tell tht i am newbie into the linux arena.

    Please educate me how uupdated pwds of the users are been changed in /etc/shadow which has only read perminssions

    Praveen Joy.

  7. Jenny Oscar Says:

    What does it mean if the password (2nd field) leaves blank or shows as “*”? Thanks.

  8. Gerald F. McMullen Says:

    In the ETC/Passwd file what functionality are the five accounts used for : Shutdown, Sync, Halt, News and Netdump ? Are these logins or are they just command files? And why don’t they have a Nologin at the end of their paths?

    Thanks Jerry

  9. vivek Says:

    nologin is shell which displays a message that an account is not available. It is intended as a replacement shell field for accounts that have been disabled or only use by system internally.

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