Host Management

The Big Picture

Think of the Total Network SolutionThink of ways to make management

easierGo with the Vendor standard install?Or Customise to suit our situation?Make all machines the same?Make all machines unique?

The Server Room

Critical hardware needs protection including:Power filter and UPSAir-conditioner, heater and fireproofingSecure access eg locked door, CCTV

monitorAnti-static fittings eg rack mount, carpetSecure cable conduits and patch panels

Start up and Shutdown

Know how to turn something off…. Before you turn it on!!

Complex systems need safe shutdown sequence to avoid damage

Quiescent state difficult to predict in multi-tasking systems

Shutdown

Complete all operations in progressPrevent new operations from startingClose filesTerminate processes and servicesSynchronise and Flush buffers/cachesDismount/park/eject disksPower off !

Shutdown Unix

Only performed by superuser halt – stops quickly and without waiting reboot – same as halt, restarts afterward shutdown – warns user first init n – where n is a run level numberBeware…. Run Level numbers are not all the same on different systems!!Eg. init5 is MultiUser mode in Redhat and PowerOff in SvR4/Solaris

PC Bootstrap SequenceAn Avalanche boot

BIOS IPL loads MBR bootMBR selects active partition

loads partition bootPartition boot can access files

loads OS loaderOS loader loads kernelKernel initialisation loads init process

Booting Unix

Machine and OS dependentUsually boots automaticallySome machine start in ROM monitor and

require a monitor command like b or bootinit

“run levels” allow several alternate configsRuns different scripts in /etc/rc.local

Booting Windows NT/2000/XP

BIOS MBR > PartitionBoot > C:\ntldr > C:\ntdetect > multiuser

C:\boot.ini allows multi-partition bootAny user can shutdown entire systemServices started according to registryNo single-user or run-levels

Workstation Personalisation

Personal workstations or NetStations?Some local storage essential

Operating systemSwap or PagefileLocal working temporary filesLocal system and user configuration

Some central shared storage needed

Disk Space Used for…

Operating system software and DataApplication software and DataShares visible to others on the NetLocal space for temporary use

Cache, print spool, transitory downloadsBackup copies

Disk partitioning

A convenient way to subdivide disk spaceReserve space for a particular function

eg swap space, user directories, softwareDisjoint storage - protection of dataEach partition given logical device name

eg C:, /dev/hda1, /dev/dsk/c0t0d0s0Meta-devices and logical volumes

seamlessly span multiple partitions

FormattingBuilding File Systems

“like painting car spaces in a carpark”Structures disk area for addressable accessUnique to OS – usually incompatible!

eg UFS not visible to Windows, NTFS not visible to UnixSectors often grouped into Allocation units

called blocks in Unix and clusters in windowsBuilding File System - mkfs or formatLabels, Directories, Free list, Data area

Unix File System

UFS disc formatiNodeDisc space allocation for each fileA Directory implementationAccess permission implementation

DOS File Allocation TableDisc formatFAT disk space management

Swap Space

Swapping – frees RAM used by an idle process by storing image on disc

Paging – virtual memory stored on discFew modern OSs actually do swappingThe swap file is now used for pagingIn Unix the swapfile is usually a partitionSwapFileSize = 2.5 * RAMsizeAny more will probably never be used!

File SystemA working system has:

Operating system files (as distributed)Other application software (packages)User filesUser Application dataTemporary working space

File SystemLogically separate because:

They have different functionsThey are owned/maintained differentlyThey change at different ratesBackup policy is different for each

File SystemA Typical Unix Layout

Operating System /boot or /kernel – boot image files /bin or /sbin – general or system executable files /dev – device files /lib – system development library files /etc – configs, params, scripts, etc… /share – common read-only files /var – non-transient workspace, logfiles /tmp or /spool – transient work and temporary files

File SystemA Typical Unix Layout

Application Software /usr /usr/local/bin /usr/local/lib /usr/local/include /usr/local/etc /usr/local/share

Unix Disk Device Names

Devices usually appear as files in /devDisks have names for each partitionPartitions may overlapBSD and SysV use different names

sd0a,sd0b,sd0c…dsk/c0t1d0s0

Contoller Target(disk) Device Segment(partition)Target or Device may be missing

System InstallationInstaller must specify…

Name, IP, subnet mask, domain, DNS IPDisc partition layout and formatSwap spaceTimezoneDirectory Service eg NIS, Windows PDCDrivers for unrecognised devices

eg Video, NIC, sound

Installing…

Solaris, Linux, Windows…Workstation, Developer and Server

versionsAll have easy installation programs

Jumpstart, Kickstart, SetupModern version auto-sense device (PnP)

and network configuration (DHCP)Installation may require license details

Configuring for use of Network Services

Host installation readies the machine for connection to the Net

Also need to have information about services provided by the Net, including:DNSNFSAuthentication (NIS, Kerberos, LDAP)

DNS configuration

Can be provided automatically by DHCPComplex setup needs more detail stored

in local files:/etc/resolv.conf

/etc/nsswitch.confUsual sequence of name search is

hosts, bind, NIS

NFS configuration

Usually requires editing of /etc/fstabAnd starting of automounter service

Multiple InstallationsBoot Managers

With multi-use machines and big disks it is possible to have several different OSs

Each OS has its own boot managerSome are generalised, some not

Eg Windows relies on files accessed from C: so install Windows first, then install Linux

Unix loaders: LILO, GRUB

Re-Installation,Multiple Installation

OS installation programs make it easy to install on a single system, but what about repeat installations or installing to large numbers of machines eg in a department of a company?

Here we need an automated process that can be given a “configuration file” and left to install in unattended mode

Multiple InstallationsImage vs Package vs Share

Image mode: writing a prepared partition image to the hard disk eg using Ghost Only possible for identical systems Difficult to change: must recreate entire image

Package: a set of dependent moduleseg compiler + libraries + templates

Package mode: installing a sequence of packages in several passes over the partition dpkg, rpm, Windows MSI, Wise, etc…

Share mode: where software is shared from server

Software Installation

Usually installed as packagesMay be distributed in limited source form

and require compilationOften installed by running a script command

configmake install

Beware of mixing versions!

Directory structure

All reliable systems separate system and application software

May also separate data from procedureUse a directory structure to achieve this

Shared Libraries (.so)Dynamic Link Libraries (.dll)

Often managed as “overlays” and loaded into RAM on demand

Managed by some kernel routines which use an “index” to locate a required module

When new versions are installed, the index must be updated (and any obsolete versions purged from RAM)

Special commands used to do this eg ldconfig