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CIT 470: Advanced Network and System Administration

CIT 470: Advanced Network and System Administration. Filesystems. Topics. Filesystems and Namespaces Filesystem Types Inodes and Superblocks Network Filesystems. Filesystems and Namespaces. Filesystems. A filesystem is a method for storing and organizing documents.

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CIT 470: Advanced Network and System Administration

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  1. CIT 470: Advanced Network and System Administration Filesystems CIT 470: Advanced Network and System Administration

  2. Topics • Filesystems and Namespaces • Filesystem Types • Inodes and Superblocks • Network Filesystems CIT 470: Advanced Network and System Administration

  3. Filesystems and Namespaces

  4. 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

  5. Kernel Storage Layers CIT 470: Advanced Network and System Administration

  6. Filesystem Tree Structure / bin boot tmp usr var bin lib X11R6 ls grub less vmlinuz bin lib zip menu.lst xclock xterm CIT 470: Advanced Network and System Administration

  7. 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

  8. Namespace contains many fs CIT 470: Advanced Network and System Administration

  9. Filesystem Types

  10. 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. CIT 470: Advanced Network and System Administration

  11. 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

  12. Inodes and Superblocks

  13. Ext Filesystem Structure CIT 470: Advanced Network and System Administration

  14. Superblocks and Block Groups CIT 470: Advanced Network and System Administration

  15. Inode Block Addressing CIT 470: Advanced Network and System Administration

  16. Journaling Filesystems Problem: writing to file involves many disk writes • Modify inode to change file size • (potentially) Add new data block to used block map • (potentially) Add pointer to new data block • Write to new data block Journaling filesystems perform writes by: • Write blocks to journal. • Wait for write to be committed to journal. • Write blocks to filesystem. • Discard blocks from journal. CIT 470: Advanced Network and System Administration

  17. Creating a Filesystem Select a disk partition to create filesystem on fdisk –l /dev/sda will list partitions on 1st disk fdisk –l /dev/sdb will list partitions on 2nd disk, Run mke2fs –v /dev/sda2 Creates ext2 filesystem on 2nd partition of 1st disk Wipes any data already existing on that filesystem Add a –j option to create an ext3 journaling fs. CIT 470: Advanced Network and System Administration

  18. Mounting a Filesystem • Create a mountpoint mkdir -p /stor/video • Mount filesystem on chosen directory mount -t ext3 /dev/sda2 /stor/video • Use filesystem • Unmount filesystem when done umount /dev/sda2 Happens automatically at reboot or shutdown CIT 470: Advanced Network and System Administration

  19. Automatic Mounting Filesystems in /etc/fstab are mounted on boot. Use mount to see current mounted filesystems. # /etc/fstab: static file system information. # # <device> <mnt pt> <type> <options> <dump> <pass> proc /proc proc defaults 0 0 /dev/sda1 / ext3 defaults 0 1 /dev/sda2 none swap sw 0 0 /dev/sda3 /home ext3 defaults 0 1 /dev/sdb1 /backup ext3 defaults 0 0 CIT 470: Advanced Network and System Administration

  20. 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

  21. 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. CIT 470: Advanced Network and System Administration

  22. 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

  23. 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

  24. Use filesystem to transparently share files. Examples: • NFSv3 • CIFS • AFS • NFSv4 Network Filesystems

  25. 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. CIT 470: Advanced Network and System Administration

  26. How NFS Works http://www.cs.ucla.edu/~kohler/class/05f-osp/notes/lec18.html CIT 470: Advanced Network and System Administration

  27. 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

  28. 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

  29. 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

  30. Client Start portmap … … … Mount filesystems. Server Start portmap Start NFS services. Configure exports. Export filesystems. Using NFSv3 CIT 470: Advanced Network and System Administration

  31. 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 CIT 470: Advanced Network and System Administration

  32. 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. CIT 470: Advanced Network and System Administration

  33. 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 CIT 470: Advanced Network and System Administration

  34. 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. CIT 470: Advanced Network and System Administration

  35. NFSv3 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

  36. /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 192.168.1.0/24(ro,all_squash) /ex/limited foo.example.com CIT 470: Advanced Network and System Administration

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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

  42. References • Michael D. Bauer, Linux Server Security, 2nd edition, O’Reilly, 2005. • Mike Eisler, Ricardo Labiaga, Hal Stern, Managing NFS and NIS, 2nd edition, O’Reilly, 2001. • 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, http://nfs.sourceforge.net/nfs-howto • RedHat, Red Hat Enterprise Linux 4 System Administration Guide, http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guide/, 2005. • RedHat, Red Hat Enterprise Linux 4 Reference Guide, http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref-guide/ch-nfs.html, 2005. CIT 470: Advanced Network and System Administration

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