Transcript Introduction - Northern Kentucky University
CIT 470: Advanced Network and System Administration Filesystems
CIT 470: Advanced Network and System Administration Slide #1
Topics
1. Filesystems and Namespaces 2. Filesystem Types 3. Inodes and Superblocks 4. Network Filesystems CIT 470: Advanced Network and System Administration Slide #2
Filesystems and Namespaces
Filesystems
A
filesystem
is a method for storing and organizing documents.
– Most filesystems offer a hierarchical tree structure of folders within folders.
– Some filesystems are flat, with no folders.
– Some filesystems work like a database, where files are identified by metadata, such as creator or user-created tags.
CIT 470: Advanced Network and System Administration Slide #4
Kernel Storage Layers
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Filesystem Tree Structure
/ bin boot tmp ls grub bin vmlinuz menu.lst
less zip usr var lib X11R6 bin lib xclock xterm CIT 470: Advanced Network and System Administration Slide #6
UNIX has One Namespace
A single tree-structured namespace which – Provides a single way to identify files by name – Contains multiple filesystems: • /dev – files represent hardware devices • /media/cdrom – ISO9660 optical media filesystem • /proc – in-memory representation of kernel data – that are added to the namespace with the mount command: mount /dev/devname /fs/location CIT 470: Advanced Network and System Administration Slide #7
Namespace contains many fs
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Filesystem Types
Filesystem Types by Media
Disk Filesystems
– Filesystems designed to store files to a fixed or removable permanent storage device.
– examples: ext4fs, FAT, ISO9660, NTFS
Solid State Filesystems
– Wear leveling: re-arrange block usage to avoid writing too many times to any one block on flash.
In-Memory Filesystems
– Filesystems that represent kernel data structures, e.g. procfs, devfs.
Network Filesystems
– Filesystems where file access operations are performed using network operations to contact a server where the data is stored on a disk or other physical medium.
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Common Disk-based Filesystems
Extended Filesystems
– – –
ext2
: first full featured UNIX fs for Linux in 1993 • Recommended use: USB + other solid state drives.
ext3
: + journaling; 2TB max file size; 16TB max vol
ext4
: faster version of ext3 with larger max file + vol size
Microsoft Filesystems
– –
FAT
: inefficient disk usage, slow, 8+3 filenames • 4GB maximum file size in 32-bit FAT
NTFS
: modern filesystem, many versions • Supports long + old 8+3 filenames for compatibility CIT 470: Advanced Network and System Administration 11
Inodes and Superblocks
Ext Filesystem Structure
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Superblocks and Block Groups
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Inode Block Addressing
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Journaling Filesystems
Problem: writing to file involves many disk writes 1. Modify inode to change file size 2. (potentially) Add new data block to used block map 3. (potentially) Add pointer to new data block 4. Write to new data block Journaling filesystems perform writes by: 1. Write blocks to journal.
2. Wait for write to be committed to journal.
3. Write blocks to filesystem.
4. Discard blocks from journal.
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Creating a Filesystem
Select a disk partition to create filesystem on fdisk –l /dev/sda will list partitions on 1 st disk fdisk –l /dev/sdb will list partitions on 2 nd disk, Run mke2fs –v /dev/sda2 Creates ext2 filesystem on 2 nd partition of 1 st disk Wipes any data already existing on that filesystem Add a –j option to create an ext3 journaling fs.
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Mounting a Filesystem
1. Create a mountpoint mkdir -p /stor/video 2. Mount filesystem on chosen directory mount -t ext3 /dev/sda2 /stor/video 3. Use filesystem 4. Unmount filesystem when done umount /dev/sda2 Happens automatically at reboot or shutdown CIT 470: Advanced Network and System Administration 18
Automatic Mounting
Filesystems in /etc/fstab are mounted on boot.
Use mount to see current mounted filesystems.
# /etc/fstab: static file system information.
# #
Checking Filesystem Integrity
fsck utility performs consistency checks – Are used blocks actually used?
– Do inodes point to any unused blocks?
– Are used inodes pointed to by directory entries?
and repairs inconsistencies if – Sysadmin enters ‘y’ in interactive mode.
– Sysadmin uses ‘-y’ argument to do all repairs.
Run fsck with unmounted partition as arg: fsck –y /dev/sda2 CIT 470: Advanced Network and System Administration 20
Access Control
Read
--You can read the file with cat , more , etc.
Write
--You can modify the file with vi ,
Execute
--You can run the file if it’s a program.
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POSIX ACLs
Specify individual groups and users.
Basic ACL user/group refers to owner.
POSIX ACLs allow specifying users + groups.
To add/modify permissions for a user: setfacl –m u:username:rw- filename To add/modify permissions for a group: setfacl –m g:groupname:rw filename CIT 470: Advanced Network and System Administration 22
File Attributes
Attributes extend file permissions: a : append-only (only root can set) i : immutable (read-only, only root can set) s : safe-delete (overwrite, not supported yet) Use lsattr to view attributes.
Most files do not have any attributes set.
Use chattr to set attributes.
chattr +i /boot/vmlinuz* CIT 470: Advanced Network and System Administration 23
Use filesystem to transparently share files.
Examples: – NFSv3 – CIFS – AFS – NFSv4
Network Filesystems
NFS v3
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 .
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How NFS Works
http://www.cs.ucla.edu/~kohler/class/05f-osp/notes/lec18.html
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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.
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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-controlled groups CIT 470: Advanced Network and System Administration Slide #28
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.
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Using NFSv3
Client
1. Start portmap 2. … 3. … 4. … 5. Mount filesystems.
Server
1. Start portmap 2. Start NFS services.
3. Configure exports.
4. Export filesystems.
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NFSv3 Services
portmap — RPC service for Linux portmap nfs — NFS file server processes.
rpc.mountd
rpc.rquotad
nfsd nfslock — Optional file locking service.
rpc.statd
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NFSv3 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.
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rpcinfo
> rpcinfo -p program vers proto port 100000 2 tcp 111 portmapper 100000 2 udp 111 portmapper 100021 1 udp 32774 nlockmgr 100021 1 tcp 34437 nlockmgr 100011 1 udp 819 rquotad 100011 2 udp 819 rquotad 100011 1 tcp 822 rquotad 100011 2 tcp 822 rquotad 100003 2 udp 2049 nfs 100003 3 udp 2049 nfs 100003 2 tcp 2049 nfs 100003 3 tcp 2049 nfs 100005 2 udp 836 mountd 100005 2 tcp 839 mountd 100005 3 udp 836 mountd 100005 3 tcp 839 mountd
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NFSv4 Processes
nfsd — NFSv4 server processes. Handles mounts.
rpc.idmapd
— Maps NFSv4 names (user@domain) and local UIDs and GIDs. Uses /etc/idmapd.conf
. rpc.svcgssd
— Server transport Kerberos auth.
rpc.gssd
— Client transport Kerberos auth.
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NFSv3 Server Configuration
1. Configure /etc/exports List filesystems to be exported.
Specify export options (ro, rw, etc.) Specify hosts/networks to export to.
2. Export filesystems.
exportfs 3. Start NFS server (if not already started) service portmap start service nfs start CIT 470: Advanced Network and System Administration Slide #35
/etc/exports
Format: directory hosts(options) Options ro, rw async Read-only, read-write.
Server replies before write.
sync all_squash root_squash Save before reply (default) Map all users to anon UID/GID.
Map root to anon UID (default) no_root_squash Don’t map root (insecure.) anon{uid,gid} Set anonymous UID, GID.
Examples: /home /backups /ex/limited *.example.com(rw,sync) 192.168.1.0/24(ro,all_squash) foo.example.com
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Client Configuration
Manual mounting mount -t
-o
:
/remote/export /local/directory
Mounting via /etc/fstab
server
:
/remote/export /local/directory
0 0 NFS Type is either nfs or nfs4 .
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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 sys — NFS security type.
uses local UIDs and GIDs.
krb5 krb5i uses Kerberos5 authentication.
uses Kerberos5 authentication + integrity checking krb5p uses Kerberos5 auth + integrity checking + encryption.
tcp, udp — Specifies protocol to use for mount.
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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 Slide #39
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.
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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.
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References
Michael D. Bauer,
Linux Server Security, 2 nd edition
, O’Reilly, 2005.
Mike Eisler , Ricardo Labiaga , Hal Stern ,
Managing NFS and NIS, 2 nd edition
, O’Reilly, 2001.
Aeleen Frisch
, Essential System Administration, 3
Evi Nemeth et al, Prentice Hall, 2001.
rd edition
, O’Reilly, 2002.
UNIX System Administration Handbook, 3 rd edition
, NFS HOWTO, http://nfs.sourceforge.net/nfs-howto RedHat, guide/
Red Hat Enterprise Linux 4 System Administration Guide
, 2005.
, http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin RedHat,
Red Hat Enterprise Linux 4 Reference Guide,
http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref guide/ch-nfs.html
, 2005.
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