1. CIT 470: Advanced Network and System Administration
Distributing Files
CIT 470: Advanced Network and System Administration

2. CIT 470: Advanced Network and System Administration
Topics
Sharing Files
Copying Files: push vs pull
rsync
Network Filesystems
Administering NFS
CIT 470: Advanced Network and System Administration

3. CIT 470: Advanced Network and System Administration
Sharing Files
System files
Centralize administration: shared logins, naming.
Solution: copy files between machines.
Alt Solution: Directory services (LDAP.)
User files
User wants access to files on every machine.
Alt Solution: Network filesystems.
CIT 470: Advanced Network and System Administration

4. CIT 470: Advanced Network and System Administration
Copying Files
Advantages
No network services to set up.
Works everywhere.
Decisions
Push vs Pull
Solutions
ftp
wget
ssh
rsync
CIT 470: Advanced Network and System Administration

5. CIT 470: Advanced Network and System Administration
Automating ftp
#!/usr/bin/expect
spawn ftp mysvr.nku.edu
expect “username:”
send “ftp\r”
expect “password:”
send
expect “ftp>”
send “bin\r”
send “prompt\r”
send “mget *\r”
send “bye\r”
expect eof
CIT 470: Advanced Network and System Administration

6. CIT 470: Advanced Network and System Administration
wget
Non-interactive file retrieval
Protocols: ftp, http, https.
Useful for automating file xfer in scripts.
Ex: wget
Options
Authentication and proxying.
Quiet
Recursive: follows links in HTTP documents.
Resume
Retries
CIT 470: Advanced Network and System Administration

7. CIT 470: Advanced Network and System Administration
ssh-based copying
Securely copy files to/from another host.
Limitations
scp copies list of files on command line (-r for recursive) to single destination.
Copies all files, not just updated files.
Must share keys to authenticate securely.
sftp most suited for manual fs exploration.
CIT 470: Advanced Network and System Administration

8. CIT 470: Advanced Network and System Administration
rsync
Synchronizes file trees between machines.
Advantages
Makes remote tree identical to local one.
Only copies files that have been changed.
Only copies file parts that have been changed.
Useful for local mirroring, staging dirs, &c too.
Transport Mechanisms
rcp: insecure, avoid.
scp: secure, commonly used.
rsync: rsync protocol, best for anonymous use.
CIT 470: Advanced Network and System Administration

9. CIT 470: Advanced Network and System Administration
rsync over ssh
Push
rsync -av -e ssh local
Pull
rsync -av -e ssh local
Test
rsync -avn -e ssh local
CIT 470: Advanced Network and System Administration

10. CIT 470: Advanced Network and System Administration
Fine tuning rsync
Deleting removed files (be careful)
rsync -av -e ssh --delete local
Excluding unwanted files.
On the command line
rsync -av -e ssh --exclude=“*.bak” --exclude=".?*.sw?” local
Through a file
rsync -av -e ssh --exclude-from=~/exclude-list local
CIT 470: Advanced Network and System Administration

11. CIT 470: Advanced Network and System Administration
rsync server
Setting up an rsync server
Create an rsyncd.conf file.
Server: rsync --daemon
Client: rsync svr::public/new.tgz .
Simple, but be careful about security.
Often secure by DNS name or IP address.
Can secure by user with rsync secrets file.
No encryption (need to use ssh tunnel.)
CIT 470: Advanced Network and System Administration

12. CIT 470: Advanced Network and System Administration
rsyncd.conf
# "global-only" options
syslog facility = local5
# global options which may also be defined in modules
use chroot = yes
uid = nobody
gid = nobody
max connections = 20
timeout = 600
read only = yes
# module: [public]
path = /home/rsync
comment = Tarball archive
hosts allow = *.nku.edu, /24,
ignore nonreadable = yes
refuse options = checksum
dont compress = *
CIT 470: Advanced Network and System Administration

13. Other File Distribution Systems
rdist
Older tool like rsync but slower, fewer features.
unison
Unlike rsync, handles updates on both sides.
Conflict resolution like CVS to handle case when file is modified on both sides.
cfengine
Maintains state of system according to policy.
Copies files as needed to meet policy.
CIT 470: Advanced Network and System Administration

14. Automating File Copying
Write a cron job.
Script can verify data before/after copy too.
How to deal with many machines?
Add a random delay using a simple script:
#!/usr/bin/perl
# sleep 0-15 minutes (0-900s)
sleep rand() * 900;
CIT 470: Advanced Network and System Administration

15. CIT 470: Advanced Network and System Administration
Network Filesystems
Idea: Use filesystem to transparently share files between computers.
Solution:
Client mounts network fs as normal.
Client filesystem code sends packets to server(s).
Server responds with data stored on a regular on-disk filesystem.
CIT 470: Advanced Network and System Administration

16. CIT 470: Advanced Network and System Administration
NFS
Network File System
Transparent, behaves like a regular UNIX filesystem.
Uses UNIX UIDs,GIDs,perms but can work on Win.
Since NFS is stateless, file locking and recovery are handled by rpc.lockd and rpc.statd daemons.
Security
Server only lets certain IP addresses mount filesystems.
Client UIDs have same permissions on server as client.
Client root UID is mapped to nobody, but
Root can su to any client UID to access any file.
CIT 470: Advanced Network and System Administration

17. CIT 470: Advanced Network and System Administration
CIFS
Microsoft Network Filesystem
Derived from 1980s IBM SMB net filesystem.
Originally ran over NetBIOS, not TCP/IP.
\\svr\share\path Universal Naming Convention
Auth: NTLM (insecure), NTLMv2, Kerberos
Implementation
MS Windows-centric (filenames, ACLs, EOLs)
Samba: UNIX client and server software.
CIT 470: Advanced Network and System Administration

18. CIT 470: Advanced Network and System Administration
AFS
Distributed filesystem
Global namespace: /afs/abc.com/vol_home1
Servers provide one or more volumes.
Volume replication with RO copies on other svrs.
Cells are administrative domains within AFS.
Cells contain multiple servers.
Each server provides multiple volumes.
Security
Kerberos authentication
ACLs with user-administered groups
CIT 470: Advanced Network and System Administration

19. CIT 470: Advanced Network and System Administration
NFSv4
New model of NFS
Only one protocol (no separate mount,lock,etc.)
Global namespace.
Security (ACLs, Kerberos, encryption)
Cross platform + internationalized.
Better caching via delegation of files to clients.
CIT 470: Advanced Network and System Administration

20. CIT 470: Advanced Network and System Administration
Adminstering NFS
NFS Versions
Using NFS
NFS Services
Server and Client Configuration
Automounter
Security
Performance
CIT 470: Advanced Network and System Administration

21. CIT 470: Advanced Network and System Administration
NFS Verions
v2 (1984) UDP 32-bit
v3 (1992) TCP 64-bit.
v4 (2000) Distributed, x-platform, security.
CIT 470: Advanced Network and System Administration

22. CIT 470: Advanced Network and System Administration
Using NFS
Client
Start portmap …
Mount filesystems.
Server
Start portmap
Start NFS services.
Configure exports.
Export filesystems.
CIT 470: Advanced Network and System Administration

23. CIT 470: Advanced Network and System Administration
NFS Services
portmap — RPC service for Linux
portmap
nfs — NFS file server processes.
rpc.mountd
rpc.rquotad
nfsd
nfslock — Optional file locking service.
rpc.statd
CIT 470: Advanced Network and System Administration

24. CIT 470: Advanced Network and System Administration
NFSv2/3 Processes
rpc.mountd — Handles client mount requests.
rpc.nfsd — NFS server processes.
rpc.lockd — Process for optional nfslock service.
rpc.statd — Handles server crashes for nfslock.
rpc.rquotad — Quotas for remote users.
CIT 470: Advanced Network and System Administration

25. CIT 470: Advanced Network and System Administration
rpcinfo
> rpcinfo -p
program vers proto port
tcp 111 portmapper
udp 111 portmapper
udp nlockmgr
tcp nlockmgr
udp 819 rquotad
udp 819 rquotad
tcp 822 rquotad
tcp 822 rquotad
udp 2049 nfs
udp 2049 nfs
tcp 2049 nfs
tcp 2049 nfs
udp 836 mountd
tcp 839 mountd
udp 836 mountd
tcp 839 mountd
CIT 470: Advanced Network and System Administration

26. CIT 470: Advanced Network and System Administration
NFSv4 Processes
nfsd — NFSv4 server processes. Handles mounts.
rpc.idmapd — Maps NFSv4 names and local UIDs and GIDs. Uses /etc/idmapd.conf.
rpc.svcgssd — Server transport Kerberos auth.
rpc.gssd — Client transport Kerberos auth.
CIT 470: Advanced Network and System Administration

27. CIT 470: Advanced Network and System Administration
Server Configuration
Configure /etc/exports
List filesystems to be exported.
Specify export options (ro, rw, etc.)
Specify hosts/networks to export to.
Export filesystems.
exportfs
Start NFS server (if not already started)
service portmap start
service nfs start
CIT 470: Advanced Network and System Administration

28. CIT 470: Advanced Network and System Administration
/etc/exports
Format: directory hosts(options)
Options
ro, rw Read-only, read-write.
async Server replies before write.
sync Save before reply (default)
all_squash Map all users to anon UID/GID.
root_squash Map root to anon UID (default)
no_root_squash Don’t map root (insecure.)
anon{uid,gid} Set anonymous UID, GID.
Examples:
/home *.example.com(rw,sync)
/backups /24(ro,all_squash)
/ex/limited foo.example.com
CIT 470: Advanced Network and System Administration

29. CIT 470: Advanced Network and System Administration
Client Configuration
Manual mounting
mount -t <nfs-type> -o <options> server:/remote/export /local/directory
Mounting via /etc/fstab
server:/remote/export /local/directory <nfs-type> <options> 0 0
NFS Type is either nfs or nfs4.
CIT 470: Advanced Network and System Administration

30. CIT 470: Advanced Network and System Administration
Mount Options
hard or soft — Error handling
hard: NFS requests will uninterruptible wait until server back.
soft: NFS requests will timeout and report failure.
intr — NFS requests can be interrupted if server unreachable.
nfsvers=2,3— NFS protocol version (not 4)
noexec — Prevents execution of binaries.
nosuid — Disables setuid for security.
rsize,wsize=# — NFS data block size (default 8192)
sec=mode — NFS security type.
sys uses local UIDs and GIDs.
krb5 uses Kerberos5 authentication.
krb5i uses Kerberos5 authentication + integrity checking
krb5p uses Kerberos5 auth + integrity checking + encryption.
tcp, udp — Specifies protocol to use for mount.
CIT 470: Advanced Network and System Administration

31. CIT 470: Advanced Network and System Administration
Automounter
Manages NFS mounts
Automounter maps vs /etc/fstab.
Mounts filesystems only when needed:
Makes administering many filesystems easier.
Improves startup speed.
Provides uniform namespaces.
Ex: mounts /home/home7 as /home on login.
/etc/auto.master points to maps
/home /etc/auto.home
Maps describe mounts
* -fstype=nfs4,soft,intr,nosuid server:/home
CIT 470: Advanced Network and System Administration

32. CIT 470: Advanced Network and System Administration
Security
Limit which hosts have access to filesystems.
Specify hosts in /etc/exports.
Use iptables to limit which hosts can use NFS.
Limit mount options
Default to ro unless writes are necessary.
Disable suid and execution unless needed.
Map root to nobody.
Block NFS at network firewalls.
Block all protocols, not just port 2049.
Use NFSv4 with Kerberos auth + encryption.
CIT 470: Advanced Network and System Administration

33. CIT 470: Advanced Network and System Administration
Performance
Measuring performance
nfsstat
/proc/net/rpc/nfsd
Optimizations
Increase the block size. Problem: fragments?
Set the async option on mounts.
Faster network card.
Faster disk array.
NVRAM cache on array to save NFS writes.
CIT 470: Advanced Network and System Administration

34. CIT 470: Advanced Network and System Administration
References
Michael D. Bauer, Linux Server Security, 2nd edition, O’Reilly, 2005.
cfengine,
Mike Eisler, Ricardo Labiaga, Hal Stern, Managing NFS and NIS, 2nd edition, O’Reilly, 2001.
expect,
Aeleen Frisch, Essential System Administration, 3rd edition, O’Reilly, 2002.
Evi Nemeth et al, UNIX System Administration Handbook, 3rd edition, Prentice Hall, 2001.
NFS HOWTO,
RedHat, Red Hat Enterprise Linux 4 System Administration Guide,
RedHat, Red Hat Enterprise Linux 4 Reference Guide,
rsync,
Unison,
CIT 470: Advanced Network and System Administration