Unreachable Remote File Systems

Provides a tutorial example on how to resolve the unreachable remote file system problem, which causes all related commands to hang, using the lazy un-mount command 'umount -l'.

Sometimes, a file system mounted from a remote server may become unreachable. This will cause any command that uses the remote file system to hang with no way to break it.

1. "df" command hangs if a remote file system is unreachable with no way to break it.

herong$ df 
(no response)

Ctr-C 
(no response)
...

2. "kill" command is not able to terminate it.

(log in from another session)
herong$ ps -efl | grep "df"
0 D herong   16317 16237  0  80   0 -  1833 smb2_r 11:11 pts/0   df

herong$ kill -9 16317 

herong$ ps -efl | grep "df"
0 D herong   16317 16237  0  80   0 -  1833 smb2_r 11:11 pts/0   df

3. Force un-mount command "umount -f" may give you an error:

herong$ mount | grep share 
  //192.168.1.100/share on /mnt/share type cifs ...

herong$ sudo umount -f /mnt/share   
  umount: /mnt/share: target is busy.

4. Only the Lazy un-mount command may resolve the problem.

herong$ sudo umount -f -l /mnt/share

herong$ mount | grep share 
  //192.168.1.100/share on /mnt/share type cifs ...

(3 minutes later)
herong$ mount | grep share 
(no output)
  
herong$ df 
(list of remaining file systems)

Note that the lazy un-mount command "umount -l" detaches the remote file system from the file hierarchy now. It may not be able to clean up all references to the un-mounted file system.

Table of Contents

 About This Book

 Introduction to Linux Systems

 Cockpit - Web Portal for Administrator

 Process Management

 Files and Directories

 Users and Groups

File Systems

 "df" - Display Free Space of File System

 Mount USB Drive as File System

 "fdisk" - Format Disk Partitions

 "dd" - Copy Data from/to Storage Devices

 Use "dd" Command to Test I/O Speed

 "hdparm" - Hard Disk Parameters

 "du" - Display Disk Usage of Directories

 Mount Windows NTFS File System

 Access Persmissions on "ntfs-3g" File System

 Mount Windows Shared Folders

 W95 Ext'd (LBA) Partition

 File System Types, IDs and Formats

 LVM (Logical Volume Manager)

 "parted" - Partition Manipulation Program

 Reformat NTFS Partition into EXT4 Partition

Unreachable Remote File Systems

 Installing CentOS

 SELinux - Security-Enhanced Linux

 Network Connection on CentOS

 Software Package Manager on CentOS - DNF and YUM

 Running Apache Web Server (httpd) on Linux Systems

 Running PHP Scripts on Linux Systems

 Running MySQL Database Server on Linux Systems

 Running Python Scripts on Linux Systems

 vsftpd - Very Secure FTP Daemon

 Postfix - Mail Transport Agent (MTA)

 Dovecot - IMAP and POP3 Server

 Email Client Tools - Mail User Agents (MUA)

 GCC - C/C++ Compiler

 Conda - Environment and Package Manager

 Tools and Utilities

 References

 Full Version in PDF/EPUB