Joshua Caltagirone-Holzli Network File System Joshua Caltagirone-Holzli

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

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

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

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

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

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

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)

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

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

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)

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

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)

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

/etc/export Format: Common options: List of options on page 491 DIRECTORY HOST1(OPTIONS) HOST2(OPTIONS) Ex: /home/jc 192.168.1.100(rw,no_root_squash) Gives root on 192.168.1.100 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

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

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

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

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

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

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

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

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