When attempting to mount a CIFS share using the standard command:

mount -t cifs //nas.domain.local/share /mnt/archive

You encounter a "Host is down" error, despite basic connectivity tests working fine:

ping nas.domain.local
smbclient //nas.domain.local/share

The discrepancy between ping/smbclient working and mount failing typically indicates one of several issues:

• SMB protocol version mismatch
• Incorrect credentials or security settings
• Outdated CIFS utilities
• Firewall blocking required ports
• DNS resolution timing issues

Solution 1: Specify SMB protocol version explicitly

mount -t cifs //nas.domain.local/share /mnt/archive -o vers=3.0

Try different versions (2.1, 3.0, 3.1.1) to find what works with your NAS.

Solution 2: Add verbose logging

mount -t cifs //nas.domain.local/share /mnt/archive -o debug

Check system logs (dmesg or /var/log/messages) for more details.

Solution 3: Test with IP instead of hostname

mount -t cifs //192.168.1.100/share /mnt/archive

This bypasses potential DNS issues.

If basic solutions don't work, consider these deeper checks:

# Check supported SMB versions
smbclient -L //nas.domain.local -m SMB3

# Verify kernel CIFS module
modprobe cifs
lsmod | grep cifs

# Test with full credentials syntax
mount -t cifs //nas.domain.local/share /mnt/archive -o username=user,password=pass,domain=DOMAIN

Once working, add to /etc/fstab for automatic mounting:

//nas.domain.local/share /mnt/archive cifs vers=3.0,credentials=/etc/smbcredentials,uid=1000,gid=1000 0 0

Create credentials file securely:

chmod 600 /etc/smbcredentials
echo "username=user
password=pass" > /etc/smbcredentials

If issues persist:

• Verify NAS firmware is updated
• Check for SELinux/AppArmor restrictions
• Test from another client to isolate the issue
• Consider Wireshark packet capture for protocol analysis

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When dealing with CIFS mounts in Linux, you might encounter a situation where:

• The mount point directory exists but shows "?" for file attributes
• Basic connectivity tests (ping, smbclient) work fine
• The mount command fails with "Host is down" error

# Example of the failing command
mount -t cifs //nas.domain.local/share /mnt/archive -o username=user,password=pass

From my experience, this typically happens due to:

1. SMB protocol version mismatch (client trying newer protocol than server supports)
2. Firewall blocking required SMB ports (445 TCP and 137-139 UDP)
3. Outdated or missing CIFS utilities
4. DNS resolution issues despite ping working

1. Force specific SMB protocol version:

mount -t cifs //nas.domain.local/share /mnt/archive -o vers=2.1,username=user,password=pass

Try different versions (3.0, 2.1, 2.0, 1.0) until it works.

2. Verify SMB ports accessibility:

telnet nas.domain.local 445
nc -zv nas.domain.local 445

3. Check CIFS utilities version:

dpkg -l cifs-utils  # Debian/Ubuntu
rpm -qa | grep cifs # RHEL/CentOS

Enable verbose logging:

mount -t cifs //nas.domain.local/share /mnt/archive -o username=user,password=pass,debug
dmesg | tail -20

Check kernel messages for CIFS errors:

journalctl -xe | grep -i cifs

For /etc/fstab entries, include protocol version:

//nas.domain.local/share /mnt/archive cifs vers=2.1,credentials=/etc/cifs.cred,uid=1000,gid=1000 0 0

Create credentials file (/etc/cifs.cred):

username=user
password=pass
domain=domain.local

If CIFS continues to fail, consider NFS or sshfs alternatives:

# NFS example
mount -t nfs nas.domain.local:/share /mnt/archive

# SSHFS example
sshfs user@nas.domain.local:/share /mnt/archive

Remember to check your server's SMB configuration (smb.conf) for any restrictions that might be causing the connection issues.