Tag: cifs

SMB/CIFS connection timeout kernel-3.10.0-957.21.3.el7

After upgrading to kernel-3.10.0-957.21.3.el7 on a CentOS server, I experienced connection timeout issues on Windows servers trying to access SMB shares. On the contrary, I was able to access the share using a Linux system without any problem.

The bug was reported in CentOS Bug Tracker and it’s caused by one of the patches applied to address CVE-2019-11478.

Some applications set tiny SO_SNDBUF values and expect TCP to just work.
Recent patches to address CVE-2019-11478 broke them in case of losses, since re-transmits might be prevented.

To (temporarily) fix this issue, I increased SO_SNDBUF value in /etc/samba/smb.conf:

socket options = TCP_NODELAY IPTOS_LOWDELAY SO_KEEPALIVE SO_RCVBUF=65536 SO_SNDBUF=65536

 

CIFS: mount error(112): Host is down

When trying to mount a Windows share using mount, I ran into this problem:

mount -v -t cifs -o username=username,password=password //hostname/sharename /mnt
mount.cifs kernel mount options: ip=XXX.XXX.XXX.XXX,unc=\\hostname\sharename,user=username,prefixpath=sharename,pass=********
mount error(112): Host is down

In my case, the error was due to a protocol mismatch when trying to mount the share: in the latest versions of Windows Server, SMBv1 is disabled.

To reach this conclusion, I ran smbclient in debug mode:

smbclient -L //hostname/sharename -U username -d 3
protocol negotiation failed: NT_STATUS_CONNECTION_RESET

To overcome this issue, I specified the protocol when using mount:

mount -t cifs -o username=username,password=password,vers=3.0 //hostname/sharename /mnt

If you want to use smbclient, add the -m option:

smbclient -L //hostname/sharename -U username -m SMB3

Mounting a Windows share using CIFS

Windows shares can be mounted using cifs option:

mount -t cifs -o username=username,password=password //hostname/sharename /mnt

By default, Windows shares are mounted with 0777 permissions in Linux.

You can change the default permissions using dir_mode and file_mode options in mount:

mount -t cifs -o username=username,password=password,dir_mode=0755,file_mode=0755 //hostname/sharename /mnt

To make the mount persistent, add the entry to /etc/fstab:

//hostname/sharename    /mountpoint   cifs  _netdev,username=username,password=password,dir_mode=0755,file_mode=0755,uid=500,gid=500 0 0