I've just rebuilt a server that had SLES10 to Slackware64 13.0.
I wanted to keep all users and their passwords, so I copied all user entries in the old SLES /etc/passwd and /etc/shadow files to the corresponding new Slackware files. It turns out that the passwords are not interpreted correctly. I presume that SLES uses a different hashing function than slackware. Is there an easy way to convert these hashes, or will I have to reset all passwords and force users to change at login?

There's an ENCRYPT_METHOD specification in /etc/login.defs which may let you use the old passwords as is. I've never tried playing with this though, so approach with caution, and probably a good idea to leave root logged onto a console while you check you can get back in.

Unless you've got hundreds of users that make it impractical, or some other technical reason you can't change the passwords then in your situation I'd be inclined to re-issue everyone with passwords. Running with a non-default password hash is the sort of thing that might pop up and bite you some time in the future when the knowledge that you'd changed it from the default has long since been forgotten.

The first part of the password hash will tell you what algorithm was used

$1$ = md5
$2$ = blowfish
$5/6$ = sha256/512

From there you can determine whether it's supported on the new OS

<edit>no... you can't convert the hashes, they're one-way hashes</edit>
cheers

Thanks GazL and kbp,

so it is $2a$10$ which I presume be some variation of blowfish.
I go by GazL's warning and will reissue new passwords.

kbp: yes, it then dawned on me that to convert them it would take the same effort as to crack them...