Created attachment 17166 [details] C-program source to reproduce the closed file problem In own environment, several Samba-servers with the parameters “workgroup = WORKGROUP” and “security = user” works correct. But the Samba-servers with the parameters “workgroup = <DOMAIN-NAME>” and “security = ads” results in a "closed file" after some hours. I expect that this disconnection is the result of an “expired Kerberos ticket”. But I don’t know how to avoid this "file closure". On a Windows-10 system the X-drive is mapped to a Samba-server in the same domain. In the attachment the C-source of a simple program is added. The C-source is compiled with gcc to the executable fwrite.exe. On that Windows-10 system the executable fwrite.exe runs for several hours correct. The output of fwrite.exe is for several hours: 8 6:57:20 fprintf ret_val = 12 fflush ret_val = 0 errno = 0 Every minute a string with day number and time is added to the file ftest_file.txt on the Samba-Server. But after several hours the output becomes: 8 16:42:23 fprintf ret_val = 12 fflush ret_val = -1 errno = 22 The file ftest_file.txt on the Samba-Server is not supplemented with date and time rules any more. The mapped X-drive is however still available. On the samba-server the command “klist” give the next output. Ticket cache: FILE:/tmp/krb5cc_0 Default principal: automation@<DOMAIN-NAME> Valid starting Expires Service principal 09/02/22 11:59:59 10/02/22 11:59:59 krbtgt/<DOMAIN-NAME>.LOCAL@<DOMAIN-NAME>.LOCAL renew until 25/02/22 11:59:59 Renewing the expire time with the command below doesn’t solve the problem. kinit -V -k -t /etc/krb5.keytab automation@<DOMAIN-NAME>.LOCAL Using default cache: /tmp/krb5cc_0 Using principal: automation@<DOMAIN-NAME>.LOCAL Using keytab: /etc/krb5.keytab Authenticated to Kerberos v5 In the Samba logfile's no relevant error messages are found. With a share on a Windows SMB-Server with SMB3 this problem doesn't occur. Doesn't a Windows SMB-server work with Kerberos? Is it possible to use Samba SMBv3 without Kerberos? The command smbstatus give "Samba version 4.7.6-Ubuntu" How can I solve this "file closure" problem?