Sunday, April 19, 2009

Ubuntu Howto | Understanding Shadow file

Ubuntu Howto - What is the "/etc/shadow" file - the file stores the actual password in encrypted format for user's account with additional properties related to user password, fields colon as a delimter.

Not all Unix systems uses the shdaow file, as some traditional Unix systems still uses the /etc/passwd to store one way encrypted password, one way of finding out if your system uses a shadow file is to check the passwd file if the foremat of it is something like the one below the chances are your using a shadow file, or just use the command "ls -la /etc/ | grep -i shadow" to see if shadow file exist, since this is an Ubuntu howto and I pressume you using an Ubuntu distribution then you are definitely using a shadow file :)


The "/etc/shadow'' file not only contains the password but also contains account expiration information, its look like the sample below


The field are seperated by colon

First feld - Username field 8 characters, its a match with the entry on passwd

Second field - Password Field 13 characters, most of the time encrypted, no entry means no password is needed to login

Third field - Number of days since password has been changed, since Jan 1, 1970.

Fourth field - Number of days before password may be change 0 indicates password can b changed anytime

Fifth field - The maximum number of days the password is valid

Sixth field - The number of days before password is to expire that user is warned that password must be changed

Seventh field - The number of days after password expires that account is disabled

Eigth field -days since Jan 1, 1970 that account is disabled i.e. an absolute date specifying when the login may no longer be used

To change your password, use the passwd command.

I hope this Ubuntu howto help you, enjoy!

More Ubuntu Howto Links below

Tech Blog Special Build your own IDS or IPS
Ubuntu Howto | Multiple IP | IP Aliasing | Howto
Ubuntu Howto - Sharing folder with Windows on Ubuntu using Samba

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