It has been a frustration for thousands of Linux users for years, that Sonos for some reason can't access a Samba share without having to create a useraccount only for this purpose. Pretty ridicilius! Even when the share has been properly configures to allowing guests, Sonos will display this message:
Here is a solution to this problem so you don't have to create a user account to access your music.
When a share in Samba is configures with the "Guest ok = yes" parameter, it's possible to acces without entering username and password. Normally. But not with Sonos. The reason is this: when you leave the "Username" and "Password" field in Sonos Setup empty, Sonos is actually using the username "guest" as user! It's not shown in the "Username" field, nor meantioned anywhere in the documentation or at the Sonos website.
So instead of accessing your music share using no username and no password, it will use the username "guest" and no password to access. And fail! A guest account is not the same as log in using the username "guest"!
The solution is: NOT to create a useraccount for Sonos, but instead tell Samba how to treat this "guest" user. Add this to your Samba configuration file smbd.conf instead:
map to guest = bad user
guest ok = yes
browseable = yes
The "map to guest = bad user" tells Samba that a unknown username should be treated as guest, and the "guest ok = yes" in [share] tells Samba to allow anonymous acces to the specifit share.
It is important to note, that a guest in Samba is not a useraccount called "guest"! In Windows there was a guest acount (a herritage from the old Windows days) called "guest" and this should not be confused with guest/anonymous login in Samba/Linux.
Samba log will generate this when trying to access a share with out any username/password. Here you can see that it uses the username "guest".
[2016/11/04 21:42:49.091294, 2] ../source3/auth/auth.c:315(auth_check_ntlm_password)
check_ntlm_password: Authentication for user [guest] -> [guest] FAILED with error NT_STATUS_NO_SUCH_USER