Passwd

For more see the man pages: [1]

/etc/shadow

This file contains the password information for users.

Ubuntu's default root entry:

root:*:15386:0:99999:7:::

Format:

username	upto 8 characters. a direct match to a line in /etc/passwd
password	blank indicates no password required. '*' indicates that password authentication for the user is disabled (e.g: use pubkey) '!' indicates that the user has been disabled (may still su to that user though) Optionally it can start with a "$" character. This means the encrypted password was generated using another (not DES) algorithm. For example if it starts with "$1$" it means the MD5-based algorithm was used. The field is then delimited by "$". The first field is the algorithm (1=MD5), the second is the salt, the third is the hashed password. openssl passwd -1 -salt SPOk02ci, enter 'hello' will result in: $1$SPOk02ci$kM3A6Yo4vJ4VGiCTx3vDX1 Use a different salt, get a different hash. Don't provide a salt to generate one!
change date	the number of days since 1 Jan 1970
change delay	the number of days before the password may be changed. 0 indicates any time
password expiry	the number of days before the user MUST change the password. 99999 indicates a long time
number of days warning	before the user will be forced to change their password
number of days before disable	after the password has epired. I assume blank is never
expiry date	number of days since 1 Jan 1970 that the account was disabled
reserved	-