SMB is the core technology for file and printer sharing. Therefore, service continuity is affected. However, after restarting the server or client, most users encounter an SMB connection failure, indicating that network resources cannot be accessed, permissions are incorrect, or the server name /IP address is invalid. How do I systematically analyze the causes of SMB restart failures? What are the specific operation solutions from basic troubleshooting to advanced recovery?

After the SMB service is restarted, it fails to connect to the server because the server process is abnormal, the configuration is reset, the network policy conflicts, or the authentication protocol is incompatible. Take an enterprise NAS device as an example. After the system is upgraded and restarted, the administrator finds that the Windows client cannot access the shared folder, but the Mac device on the same network is connected properly. The initial check shows that the SMB service process is started and the communication between the IP address and port is normal. Further analysis shows that the NTLMv2 authentication enabled by default in Windows conflicts with the NAS SMB configuration (only NTLMv1 is supported), resulting in a protocol handshake failure. You need to determine this problem based on the service status, network policy, and log information.

The core solution requires a service process and a self-starting configuration first. A common cause is that the SMB service does not run automatically after the restart. In Linux, if systemd is used to manage services, check the self-starting status of the smb (Samba) and nmb (NetBIOS) services.

Check service status

systemctl status smb nmb

Enable self-start and start the service immediately

systemctl enable now smb nmb

For older Linux distributions (such as CentOS 6), you need to add a startup command in /etc/rc.local to ensure loading after restarting:

/etc/init.d/smb start
/etc/init.d/nmb start

In Windows, if the Server service is not started, run the following command to restart it:

powershell
net stop LanmanServer /y
net start LanmanServer

A firewall rule reset may block SMB communication ports (TCP 139/445, UDP 137/138). Linux systems need to open ports and override rules:

firewallcmd permanent addservice=samba
firewallcmd reload

If SELinux is enabled, Boolean values need to be adjusted to allow SMB sharing:

setsebool P samba_enable_home_dirs on
setsebool P samba_export_all_rw on

Temporarily turning SELinux off quickly verifies that it is a policy intercept (use with caution in production environments) :

setenforce 0

New versions of Windows disable SMBv1 by default, while older devices, such as iot terminals or certain NAS, may only support lower versions of the protocol. On the Windows client, you can select SMBv1 support by enabling or disabling Windows Features. For macOS, if the connection fails due to incompatible protocol versions, modify the /etc/nsmb.conf file to force a later version of the protocol.

[default]
protocol_vers_map=3 Change the version from 1 to 3 to accommodate a new server

Authentication protocol mismatch will trigger permission errors in domain environments or cross-platform access. On a Windows client, you can adjust local security policies to be compatible with the authentication mode of an earlier version: Run secpol.msc to navigate to Local Policies → Security Options. Change Network Security: LAN Manager Authentication Level to Send LM and NTLM responses. The shared folder permissions must be synchronized with the Samba configuration file (smb.conf) to ensure that users or groups have read and write permissions:

bash
[shared_folder]
path = /data/share
valid users = @smbusers
writable = yes

Static IP addresses may become invalid after the restart due to DHCP assignment conflicts. You are advised to bind MAC addresses to the NAS or server, or use dynamic IP addresses on the client. If access through the host name fails, try to connect directly using the IP address (such as \\192.168.1.100). For intermittent access failure of devices such as Android TV, you can periodically clear the client cache:

cmd
net use /del /y Windows Clears the network mapping cache

The Samba log (/var/log/samba/log.%m) and the Windows Event Viewer (event ids 3019, 3045) are key to locating the problem. For example, if the message NT_STATUS_ACCESS_DENIED is displayed, the user permission configuration is incorrect. If TCP RST Reset Connection is frequently displayed, check the session persistence policy of network devices such as switches or update system patches.

Code example: Automatic detection script

The following Python script automatically detects SMB service status and port connectivity:

python
import socket
import subprocess
def check_smb_service():

Check the status of the Linux Samba service

try:
status = subprocess.check_output("systemctl isactive smb", shell=True).decode().strip()
return status == "active"
except:
return False
def test_smb_port(ip):

Example Test the availability of the SMB port

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(3)
try:
sock.connect((ip, 445))
return True
except:
return False
finally:
sock.close()

Example: Detect the local SMB service and test the port

if check_smb_service() and test_smb_port("127.0.0.1"):
print("SMB service running properly ")
else:
print(" Exception exists, please check service and firewall ")

After the SMB service restarts, connection faults are the result of dynamic changes in server configurations, network policies, and system environments. The fault is rectified layer by layer, from basic service status check to protocol version adaptation to in-depth log analysis. Monitoring tools can be deployed to track SMB status, combined with automated scripts to periodically verify port availability. In addition, regular backups of the Samba configuration file (smb.conf) and Windows registry keys (such as HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer) enable quick recovery in the event of configuration loss, minimizing service outage.