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):
- Username: It is used when user logs in. It should be between 1 and 32 characters in length.
- Password: An x character indicates that encrypted password is stored in /etc/shadow file.
- 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.
- Group ID (GID): The primary group ID (stored in /etc/group file)
- 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.
- 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 /
- 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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Related Other Helpful FAQs:
- How To: UNIX Add A User To A Group
- Howto: Linux Add User To Group
- Understanding /etc/shadow file
- What does a plus + at the beginning of a line in the /etc/passwd UNIX / Linux password file signify?
- Why and How To Customize a UNIX / Linux User Account?
Discussion on This FAQ
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February 19th, 2007 at 6:47 am
What are the differences between system calls and Library functions?
March 12th, 2007 at 9:28 am
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/
March 14th, 2007 at 8:30 pm
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.
October 1st, 2007 at 2:17 am
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
October 1st, 2007 at 2:19 am
That was /etc/passwd
February 26th, 2008 at 9:31 pm
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.
May 14th, 2008 at 1:45 am
What does it mean if the password (2nd field) leaves blank or shows as “*”? Thanks.
June 4th, 2008 at 3:39 pm
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
June 4th, 2008 at 3:46 pm
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.