Samba troubleshooting

Samba can be a real pain when it wants to be, occasionally, for seemingly no reason at all it stops working (after service restart), and then maybe 30min later, with no configuration changes it just starts working again. Below are some of the ways that I have (very unscientifically) gotten around it.

Troubleshooting Tools

iftop	show network activity on interface
nfsstat	show r/w operations on NFS filesystems
cifsstat	show r/w operations on CIFS filesystems
smbclient	list shares on ip-addr (see usage)

Verify Shares Available

sudo smbclient \
     -L //127.0.0.1 \
     -U login-user \
     --list

Debugging Error Codes

NOTE:

understanding not confirmed

Mount errors are visible in dmesg.
The error code produced combines bitwise OR flags.

# man mount

RETURN CODES
mount has the following return codes (the bits can be ORed):

0      success
1      incorrect invocation or permissions
2      system error (out of memory, cannot fork, no more loop devices)
4      internal mount bug
8      user interrupt
16     problems writing or locking /etc/mtab
32     mount failure
64     some mount succeeded

Say we get the error:

[   10.361390] CIFS: Attempting to mount //192.168.1.220/audiobooks
[   10.361439] CIFS: VFS: Error connecting to socket. Aborting operation.
[   10.361442] CIFS: VFS: cifs_mount failed w/return code = -101

We can deconstruct the error-code into specific errors

# error code was '-101'
bin(101)  
>>> 0b1100101
#      \\  \ \
#       \\  \ +-- incorrect invocation or permissions
#        \\  +-- internal mount bug
#         \+-- mount failure
#          +-- some mount succeded

Large File Copy Hangs

explicitly set SMB protocol version to 3.0 fixed this entirely for me.

mount //server/mount  /mnt/mounted  -o vers=3.0

No Write Permissions

There are a few possible causes:

1. writing files is not allowed in smb.conf
2. directories/files on server not writable by samba's login user
3. directories/files on client not owned by user/assigned appropriate permissions

Frozen following Sleep/Suspend

Use systemd sleep hooks to unmount remote filesystems on sleep.

# /etc/systemd/system/unmount-remotefs.service

[Unit]
Description=unmount remote filesystems before sleep
Before=sleep.target
StopWhenUnneeded=yes

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=umount -a -t cifs
ExecStop=mount -a -t cifs

[Install]
WantedBy=sleep.target

Cannot load DLLs in share

For windows to load a .dll, it needs 'rw' permissions.

You can manually adjust the real file permissions (preferred), but if you are in an environment where this cannot be done, you can force the shares to mount as a user that has rw permissions on the file.

[your_share]
force user=root  # or preferably owner of shares