When mounting CIFS shares, using a credentials file is generally considered more secure than passing credentials directly in the command line. However, a common pitfall occurs when passwords contain special characters that might be interpreted differently by the shell and the credentials parser.

The original attempt fails with an "Access Denied" error:

mount.cifs //server/share /mnt/share -o credentials=credfile

Credentials file content:

username=Administrator
password=What@zR\!p3s

Interestingly, the direct command-line approach succeeds:

mount.cifs //server/share /mnt/share -o username=Administrator,password=What@zR\!p3s

The discrepancy stems from how special characters are processed:

• In the credentials file, backslashes might be treated as escape characters during file reading
• When passed directly, the shell handles the escaping differently
• The bang (!) character can cause additional interpretation issues

Here are several approaches to resolve this:

1. Double Escaping in Credentials File

username=Administrator
password=What@zR\\!p3s

2. Using Single Quotes in Command Line

mount.cifs //server/share /mnt/share -o credentials='credfile'

3. URL Encoding Special Characters

username=Administrator
password=What%40zR%5C!p3s

4. Creating a Helper Script

#!/bin/bash
MOUNT_POINT="/mnt/share"
SHARE="//server/share"
CRED_FILE="/path/to/credfile"

mount.cifs "$SHARE" "$MOUNT_POINT" -o "credentials=$CRED_FILE"

• Always set strict permissions (chmod 600)
• Consider using a dedicated credentials directory
• Test with simple passwords first when troubleshooting
• Check system logs for additional error details

For persistent mounts, consider adding to /etc/fstab with proper escaping:

//server/share  /mnt/share  cifs  credentials=/path/to/credfile,uid=1000,gid=1000,file_mode=0644,dir_mode=0755  0  0

Or use environment variables in a wrapper script:

export CIFS_USER="Administrator"
export CIFS_PASS="What@zR\\!p3s"
mount.cifs //server/share /mnt/share -o user=$CIFS_USER,pass=$CIFS_PASS

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When working with CIFS mounts on XenServer 5.6 FP1, many administrators encounter authentication failures when special characters appear in the password field of credentials files. The specific error manifests as:

mount.cifs //server/share /mnt/share -o credentials=credfile
# Returns: "Access Denied"

Yet the direct credential passing works:

mount.cifs //server/share /mnt/share -o username=Administrator,password=What@zR\\!p3s
# Succeeds

The credentials file parsing in older CIFS implementations has known issues with:

• Special characters (@, !, \, etc.)
• Backslash escaping sequences
• Newline handling

A typical credentials file structure:

username=value
password=value
domain=value

Method 1: Character Escaping in Credentials File

For passwords containing special characters, try these variants in your credentials file:

# Option 1: Double escaping
password=What@@zR\\!p3s

# Option 2: Hex encoding
password=What\x40zR\x5C\x21p3s

# Option 3: Single quotes
password='What@zR\!p3s'

Method 2: Environment Variables

Create a wrapper script:

#!/bin/bash
export CIFS_PASS="What@zR\\!p3s"
mount.cifs //server/share /mnt/share -o username=Administrator,pass="${CIFS_PASS}"

Method 3: Direct Mount Options

When possible, pass credentials directly:

mount -t cifs //server/share /mnt/share \
  -o username=Administrator,password=What@zR\\!p3s,sec=ntlmssp

• The bundled CIFS version (5.6 FP1) uses legacy parsing
• Consider upgrading to newer XenServer versions
• Test with different security options: sec=ntlm,sec=ntlmssp,sec=ntlmv2

Enable verbose logging:

mount.cifs -v //server/share /mnt/share -o credentials=credfile,debug=1

Check system logs:

dmesg | tail -20
journalctl -xe