[Samba] Randomly occurring file losses on samba share

[Andreas Huppert]

Hello,

further investigating the problem we were able to provoke an issue that might be related to the initial problem and could be reproduced with a higher likelihood. The core of the reproducible problem is, that sometimes a file is being created by an application running on the client, but then cannot be written to. Therefore the application throws permission related errors and documents cannot be saved.

We believe, that this behavior may also has caused the problem with the disappearing files (in connection with the weird file saving procedure of MS Word), but of course, we can’t say that for sure. Explaining in brief: Word creates a temp file with the new content, then renames the original file to a temporary file, renames first temporary file to the original's name and deletes the second temporary file afterwards.

However: While writing to a new file (saving), according to the logs, they seem to be opened with read permissions only, but still get created with a size of 0 byte.

We tried to narrow down the problem and therefore turned off all file locking mechanisms provided by samba:
locking = no
strict locking = no
oplocks = no
kernel oplocks = no
fake oplocks = no
blocking locks = no
level2 oplocks = no
posix locking = no

We observed that the number of occurrences decreased, but unfortunately the problem still persists.

Next we investigated access rights. As mentioned before, permissions are controlled via ACLs.
getfacl on the directory we were testing in, gives the following output:
# file: /path/to/folder
# owner: root
# group: root
# flags: -s-
user::rwx
user:root:rwx
group::rwx
group:root:rwx
group:group1:rwx
group:group2:rwx
mask::rwx
other::---
default:user::rwx
default:user:root:rwx
default:group::rwx
default:group:root:rwx
default:group:group1:rwx
default:group:group2:rwx
default:mask::rwx
default:other::—

Related options in smb.conf are:
invalid users = root xxxx
inherit acls = yes
inherit permissions = yes
map acl inherit = no
inherit owner = yes

According to the log files, permission don’t seem to be the problem, although we expected returning 0770. But for the client user always having ownership of the files, group permissions should not matter:
unix_mode(/path/to/annoy.docx) inheriting from /path/to
Apr 10 16:16:19 fileserver smbd[2148]:   unix_mode(/path/to/annoy.docx) inherit mode 42770
Apr 10 16:16:19 fileserver smbd[2148]:   unix_mode(/path/to/annoy.docx) returning 0760

Simply put, we are still kind of clueless and highly appreciate any hints/help.

Best regards,

Andreas Huppert

Am 08.04.2015 um 18:34 schrieb Andreas Huppert <samba-srv at kemper-schlomski.de>:

> Hello,
> 
> having migrated from OSX Server with AFP filesharing, we've experienced a problem with randomly occurring file losses on our samba server. Due to the fact we were not able to reproduce the problem reliably, we are quite clueless what could cause this behavior and therefore desperately looking for any hints.
> 
> The Server in question is running Ubuntu 14.04LTS with the Version of Samba being '4.1.6+dfsg-1ubuntu2.14.04.7'. It is set up to retrieve its users from an LDAP directory using libnss-ldapd while authentication is done via Kerberos. File permissions are controlled by POSIX-ACLs on top of an ext4 filesystem.
> 
> On the client side, there are clients running Mac OSX 10.9.5 or Mac OSX 10.10.2. The connection to the server is established using built-in 'Finder' functions.
> 
> Server and clients are provided with latest updates.
> 
> The Problem was recognized while working on MS Office documents, whereby the affected documents were first saved and closed by one client, later opened by another client (while the first client was still connected to the share), and disappeared shortly after the second client saved (and closed) the edited file. The file can be restored via extundelete but then may contain content of another file. (In a particular example a restored .docx file contained content of a .xlsx file that was edited in a timely manner on the same share).
> 
> We're unsure whether the problem is located in Finder, MS Office or samba itself, but quite confident it is related to the new samba environment, because this behavior was never observed before, with nearly identical share structure, when AFP was used. Maybe it's worth to note that normal users are not allowed to write to the first level of a share.
> 
> Relevant config-files are written down below.
> 
> Kind regards,
> 
> Andreas Huppert
> 
> 
> 
> Client configuration:
> #/etc/nsmb.conf
> [default]
> smb_neg=smb2_only
> 
> 
> Server configuration:
> #/etc/samba/smb.conf
> workgroup = WORKGROUP
> server string = %h server (Samba, Ubuntu)
> dns proxy = no
> log file = /var/log/samba/samba.log
> max log size = 10000
> syslog = 10
> syslog only = yes
> log level = all:1
> ldap ssl = start tls
> disable netbios = yes
> usershare allow guests = no
> 
> security = ADS
> realm = REALM
> kerberos method = dedicated keytab
> dedicated keytab file = /etc/samba/keytab.keytab
> 
> nt acl support = yes
> hide unreadable = no
> encrypt passwords = yes
> obey pam restrictions = no
> unix password sync = no
> ldap ssl ads = yes
> 
> invalid users = root xxxx
> inherit acls = yes
> inherit permissions = yes
> map acl inherit = no
> inherit owner = yes
> 
> [Share]
> path = /path/to/share
> writeable = yes