Common UNIX administration tasks

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Common UNIX administration tasks
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Backups

• The correct management of backup policy is
  possibly the most important role of a systems
  administrator
• It serves to provide
• Archives of data and state, roll-back, comparison
• Disaster recovery plan
• System replication mechanism
• Software deployment mechanism

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Backup Restore

• Traditionally backup is to tape devices for
  reasons of capacity and reliability
• Backup may be to any other device depending on
  factors such as
• Capacity
• Speed
• Reliability
• Facility
• Cost
• Cost

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tar

• Oldest UNIX backup method, runs on all UNIX
  variants
• Supports appending of files to the end of the
  tape
• Very slow, not really suitable for full system
  backups

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tar

• To create an archive with everything in the
  current directory (onto the device /dev/rmt/0m)
• tar cvf /dev/rmt/0m .
• To extract all file from the archive
• tar xvf /dev/rmt/0m
• To extract named files from an archive called
  archive.tar
• tar --extract --filearchive.tar myfile
• To list the contents of an archive
• tar --list --verbose --file/dev/rmt/0m

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cpio

• Much faster than tar
• Good for replicating directory trees
• Supports incremental backup
• Copy all files in the current directory and put
  them into the file called archive
• find . cpio o F archive
• Extract files from the file called archive
• cpio i F archive

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dd

• Bit-for-bit copy
• Does not copy files and ownerships, just copies
  bits
• Cannot select files and directories from a dd
  tape
• Used for creating mirror images of disks at a low
  level

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dump / ufsdump

• Used for creating full or incremental backups
• Can specify levels for dumping which specify the
  type of incremental backup
• Level 0 full backup
• Level 1 all files changed since last level 0
  dump
• Level 2 all files changed since last level 1
  dump
• Etc.

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Backup Types

• Full
• Backup everything on the system
• Incremental
• Backup only those files that have changed since
  the last full backup
• Differential
• Backup only those files that have changed since
  the last backup

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Grand Father - Father - Son Backup Scheme

• Perform an initial Full System Backup
• Perform daily backups, Monday, Tuesday,
  Wednesday, Thursdayreuse these tapes each week
• Perform weekly backups Friday1, Friday2,
  Friday3reuse these tapes each month
• Perform monthly backups Month1, Month2 etc.

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Grand Father - Father - Son Backup Scheme

• Files can be restored to within 1 day, for files
  archived within the last week
• Files can be restored to within 1 week for files
  archived within last month
• Files can be restored to within 1 month for files
  archived within last year

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Scheduling Backups

• Cron is the UNIX scheduling daemon
• The windows environment includes the Scheduler
  service which can be accessed using the At command

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Cron (unix)

• Depending on the system configuration, users may
  schedule tasks to occur at specific times on a
  UNIX system
• The cron service searches the /var/spool/cron
  directory for cron files
• Cron files are named after usernames in
  /etc/passwd
• Files specify the time and the command to perform

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Cron (unix)

• The cron service wakes up every minute and
  examines all the cron files
• Within each file it examines each line to
  ascertain if a command needs to be executed
• When the command is executed, any output is
  mailed to the user who owns the file or the
  username (if any) specified in the command

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Cron (unix)

• Format of the crontab files
• minute (0-59)
• hour (0-23)
• monthday (1-31)
• month (1-12)
• weekday (0, Sunday 6, Saturday)
• username
• Command

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Cron (unix)

• Example
• ls l /etc gt /home/rbradley/etclist.txt
• 0 2 6 full-backup
• 15 12 1-5 incremental-backup
• 0 3 0 find / -name core atime 7 gt /corelist
• 0,20,40 0,6 who gtgt /home/rbradley/wholog
• 0,10,20,30,40,50 1-5 w gtgt
  /home/rbradley/wholog

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Cron (unix)

• edited with crontab e
• displayed with crontab l
• deleted with crontab -r

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At (unix)

• Used for single command execution at 900pm
  atgt find / -name core exec rm \

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At (windows)

• at \\computername time /interactive
  /everydate,... /nextdate,... command
• at 1527 wholog.bat
• at 1700 /nextF collectCSAA.bat
• at 0300 /everyM,T,W,Th incBackup.bat
• at 0300 /everyF fullBackup.bat

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NFS

• Network File System

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Network File Systems

• Network file systems allow us to share files
  between users on different systems, often with
  different operating systems
• The Windows operating systems use CIFS (SMB)
  network file system as implemented by the Samba
  package on UNIX systems

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NFS Service Profile

• Type System-V managed service
• Package nfs-utils
• Daemons nfsd, lockd, rpciod, rpc.mountd
  rpc.rquotad, rpc.statd
• Scripts nfs, nfslock
• Ports assigned by portmap (111)
• Configuration /etc/exports

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Packaging for Unix/Linux

• Different packaging approaches
• Solaris Pkg (pkginfo, pkgadd, pkgmake)
• Linux rpm / rpmbuild
• Uses digital signatures
• Overall objectives and approaches are similar
• Packages are created

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NFS (Network File System)

• Developed by Sun Microsystems
• Uses the RPC (remote procedure call) service
• Requires portmap
• Directories shared through the /etc/exports file
• Directories mounted through the mount command

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NFS Server Components

• portmap maps calls from other machines to the
  correct RPC service
• nfs kernel module translates NFS requests into
  local file system requests
• rpc,mountd file client used to mount and unmount
  remote file systems

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/etc/exports examples

• /var/ftp/pub .dit.ie(ro,sync)
  .comp.dit.ie(rw,sync)
• /root/presentations rbradley.dit.ie(rw,sync)
• /data 147.252.230.230(sync)
• Note that whitespace makes a difference
• server(options) applies the options to that
  server
• server1 (options) applies the options to
  everything apart from the server

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/etc/exports

• Exported with root-squashing turned on, this
  ensures that requests from the root user on a
  client machine are denied root access to
  root-owned files on a server machine
• Such requests are mapped onto a uid such as 65534
• Can be prevented with the no_root_squash option,
  but this is not recommended

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/etc/exports examples

• More examples
• /usr/local 192.168.0.1(ro) 192.168.0.2(ro)
• /home 192.168.0.1(rw) 192.168.0.2(rw,
  no_root_squash)
• Also allow access to sets of computers
• /usr/local 192.168.0.0/255.255.255.0(ro)
• /home 192.168.0.0/255.255.255.0(rw)

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Controlling access

• Most services (anything controlled by inetd and
  also nfs) support access control with
  /etc/hosts.allow, /etc/hosts.deny
• Format of files isservice name host or
  network/netmask, host or network/netmask
• E.g
• portmap 192.168.0.1 , 192.168.0.2
• mountd 192.168.0.1 , 192.168.0.2
• All all

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Controlling access

• Any service using this approach will follow the
  process
• Check in hosts.allow if the requesting server is
  in this file, allow the access and finish
• Now check in hosts.deny, if the requesting server
  is not in this file, allow the access and finish.
• Allow access
• For nfs, to allow/deny access ALL the services
  need to be included in the file.
• portmap, lockd, mountd, rquotad, statd

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NFS Client

• Client side NFS implemented as a kernel module
• /etc/fstab used to specify network mounts.
• NFS shares are mounted at boot time by
  /etc/rc.d/init.d/netfs

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NFS Client

• Shares can be mounted manually by root, or
  automatically at boot time.
• The default /etc/fstab nfs entries in UML
• Device mountpoint type options dump
  fsckorder
• /dev/ubd/0 / ext2 defaults
  1 1
• /proc /proc proc defaults
• /dev/ubd/1 none swap sw
• /etc/fstab nfs entry
• Device mountpoint type options dump
  fsckorder
• Server1/var/ftp/pub /mnt/pub nfs defaults 0 0

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NFS Mount Options

• Options include
• rsize8192 and wsize8192 will speed up transfers
  considerably
• soft processes return with an error on a failed
  I/O attempt
• hard will block a process that tries to access
  an unreachable share.
• nolock disables file locking and allows inter
  operation with older NFS servers
• nosuid stops suid enabled programmes executing
  from the mounted file system.
• noexec stops all programmes executing from the
  mounted file system.
• ro read only mount point

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NFS autofs

• autofs provides the ability to mount NFS shares
  on demand and to unmount them when they are idle
• autofs uses the files /etc/auto.master and
  /etc/auto.misc for configuration
• autofs is a kernel service, but must be enabled
  by configuring autofs to run in the appropriate
  run levels

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NFS Services

• exportfs r refreshes the servers share list
  after modifying /etc/exports
• -v displays a list of the shared directories and
  options on a server
• -a exports all shares listed in the /etc/exports
  or a share named as an argument
• -u unexports the share named as an argument or
  all shares with no argument and a a
• -e host shows the available shares on host

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Trouble shooting nfs

• Unable to see a mounted file system
• cat /proc/mounts
• mount f
• Permission denied on mount attempt
• Check that the fstab entry and exports have the
  same access (i.e. ro, rw etc)
• Check you havent attempted to export both a
  parent and a child
• i.e. /usr and /usr/local cant be both exported.

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Trouble shooting nfs II

• RPC Program not registered
• On the server, use ps or rpcinfo p to check that
  portmapper, nfs and mountd are running
• On the client, use rpcinfo p server to check
  that it can see the services
• If the client gets No Remote programs registered,
  check hosts.allow and hosts.deny

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Trouble shooting nfs III

• Permissions arent right
• /export/dir hostname(rw,no_root_squash)
• /export/dir hostname (rw,no_root_squash)
• These statements arent the same. White space in
  the second will mean that everybody apart from
  hostname will get the privileges in the ().

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NFS optimisation

• Issues
• NFS is sensitive to network traffic
• NFS needs both read and write performance
• NFS traffic is bursty
• Detection
• /usr/sbin/nfsstat n -a

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NFS optimisation

• Lower the nice value
• Spread NFS exported file systems across multiple
  disks and disk controllers.
• Use RAID 0 for read/write intensive
• Use RAID 1 for read intensive
• Reduce the number of write intensive mounts
• Automount is difficult to get away from