1. Joshua Caltagirone-Holzli
Network File System
Joshua Caltagirone-Holzli

2. Overview Introduction to NFS Features General Information Server Side
Client Side
Automount

3. Introduction to NFS NFS – Network File System
In widespread use in many organizations
Developed by Sun
Implemented over Sun Remote Procedural Call
Uses either TCP or UDP

4. Features File Locking Disk Quotas Cookie and Stateless Mounting
Security and NFS

5. File Locking File locking Daemons NFS utilizes
Traditional System Calls
Flock, lockf, fcntl
Daemons NFS utilizes
Lockd
Statd
NFS file locking is still shakey

6. Disk Quotas NFS enforces underlying file system quotas
Daemon for user stats
Rquotad
Disk quotas considered obsolete

7. Cookies and Stateless Mounting
Clients must explicitly mount an NFS filesystem
NFS is stateless
Does not keep track of who mounts a file system
NFS “cookies”
Sent at conclusion of successful mount
Identifies the mounted directory

8. Cookies and Stateless Mounting
Unmounting/Remounting changes cookies
Means cookies are saved across reboot
Server crashes cause NFS to resume as normal
Cookie uses RPC file/dev IO
Client responsible for acknowledging server before removing local file (writing)

9. Security and NFS /etc/exports
Provides access to NFS volumes
This file enumerates the hostnames of systems who have access to the file system
Export file systems only to clients you trust
Access to NFS ports should be restricted

10. Security and NFS File level access on NFS based on:
UID, GID, and file permissions
NFS servers trust the client to tell who is accessing flies
Example: if mary and bob have the same UID then they are able to access each other’s files

11. Security and NFS
Root_squash – prevents root from changing the UID on the NFS server
Forces root to be a normal user on the server
Block access to portmap (port 111)

12. General Info
Users should usually be given the same UID on all machines
Anonuid/anonguid – used to change the UID/GID mappings for root
All_squash – forces all clients to have the same UID/GID on the server
No_root_squash – turns off UID mapping for root
Used for diskless systems

13. Server Side NFS Mountd – handles mount requests
Nfsd – handles the actual file access requests
Both should start when the system starts
Typical startup scripts:
/etc/rc.d/init.d/nfs (Red Hat/Fedora)
/etc/init.d/nfsboot (SUSE)
/etc/init.d/nfs-* (Ubuntu/Debian)

14. Server Side NFS Exportfs – used to add and modify entries for sharing
Exportfs –u (to remove entries)
Exportfs –a (to update export after writing to config /etc/exports)
/etc/exports – typical location for this file
Hosts.allow/hosts.deny
Give hosts access to NFS server

15. /etc/export Format: Common options: List of options on page 491
DIRECTORY HOST1(OPTIONS) HOST2(OPTIONS)
Ex: /home/jc (rw,no_root_squash)
Gives root on full access of this directory
Common options:
Subtree_check – verifies that all file requests are within the exported subtree
Async – makes server repiles to write requests before actually writing
Unhide – revleas filesystems mounted within exported file trees
List of options on page 491

16. Client Side NFS Mounted the same way as normal file systems
Mount command understands notion hostname:dicrectory
Showmount –e SERVER
Command allows client to verify that server has properly exported file systems

17. Example Mount Mount –o rw,hard SERVER:/PATH /LOCALPATH
Hard – causes all operations who are accessing the server to stop if the server crashes until it is back up again
More mount options on page 493

18. Client Commands Df – works are normal
Umount – cannot unmount an NFS volume unless it is not in use
lsof

19. /etc/fstab Can mount NFS volumes with fstab Set fstype to nfs
File system should be SERVER:/PATH
Flags would be nfs options

20. NFS Stats Nfsstat – displays various stats of the NFS system
shows server side processes
Nfsstat –c
shows client side processes

21. Automounting /etc/init.d/autofs /etc/auto.master
Startup script for automount daemon
/etc/auto.master
Main file for holding the map information
Format:
/DIRECTORY /MAP/POINT +/- OPTIONS

22. Conclusion Introduction to NFS Features General Information
Server Side
Client Side
Automount

23. Are there any questions???
The End
Are there any questions???