AIX GLOBAL

List the licensed program productslslpp -LList the defined devices lsdev -C -HList the disk drives on the system lsdev -Cc diskList the memory on the system lsdev -Cc memory (MCA)List the memory on the system lsattr -El sys0 -a realmem (PCI)lsattr -El mem0List system resources lsattr -EHl sys0List the VPD (Vital Product Data) lscfg -vDocument the tty setup lscfg or smit screen capture F8Document the print queues qchk -ADocument disk Physical Volumes (PVs) lspvDocument Logical Volumes (LVs) lslvDocument Volume Groups (long list) lsvg -l vgnameDocument Physical Volumes (long list) lspv -l pvnameDocument File Systems lsfs fsname/etc/filesystemsDocument disk allocation dfDocument mounted file systems mountDocument paging space (70 - 30 rule) lsps -aDocument paging space activation /etc/swapspacesDocument users on the system /etc/passwdlsuser -a id home ALLDocument users attributes /etc/security/userDocument users limits /etc/security/limitsDocument users environments /etc/security/environDocument login settings (login herald) /etc/security/login.cfgDocument valid group attributes /etc/grouplsgroup ALLDocument system wide profile /etc/profileDocument system wide environment /etc/environmentDocument cron jobs /var/spool/cron/crontabs/*Document skulker changes if used /usr/sbin/skulkerDocument system startup file /etc/inittabDocument the hostnames /etc/hostsDocument network printing /etc/hosts.lpdDocument remote login host authority /etc/hosts.equi

This chapter describes the boot process and the different stages the systemuses to prepare the AIX 5L environment.Topics discussed in this chapter are: The boot process System initialization The /etc/inittab file How to recover from a non-responsive boot process Run levels An introduction to the rc.* files

The fundamental concepts used by LVM are physical volumes, volume groups,physical partitions, logical volumes, logical partitions, file systems, and rawdevices. Some of their characteristics are presented as follows: Each individual disk drive is a named physical volume (PV) and has a namesuch as hdisk0 or hdisk1. One or more PVs can make up a volume group (VG). A physical volume canbelong to a maximum of one VG. You cannot assign a fraction of a PV to one VG. A physical volume isassigned entirely to a volume group. Physical volumes can be assigned to the same volume group even thoughthey are of different types, such as SCSI or SSA. Storage space from physical volumes is divided into physical partitions (PPs).The size of the physical partitions is identical on all disks belonging to thesame VG. Within each volume group, one or more logical volumes (LVs) can be defined.Data stored on logical volumes appears to be contiguous from the user pointof view, but can be spread on different physical volumes from the samevolume group. Logical volumes consist of one or more logical partitions (LPs). Each logicalpartition has at least one corresponding physical partition. A logical partitionand a physical partition always have the same size. You can have up to threecopies of the data located on different physical partitions. Usually, physicalpartitions storing identical data are located on different physical disks forredundancy purposes. Data from a logical volume can be stored in an organized manner, having theform of files located in directories. This structured and hierarchical form oforganization is named a file system. Data from a logical volume can also be seen as a sequential string of bytes.This type of logical volumes are named raw logical volumes. It is theresponsibility of the application that uses this data to access and interpret itcorrectly. The volume group descriptor area (VGDA) is an area on the disk that containsinformation pertinent to the volume group that the physical volume belongs to.It also includes information about the properties and status of all physical andlogical volumes that are part of the volume group. The information from VGDAis used and updated by LVM commands. There is at least one VGDA perphysical volume. Information from VGDAs of all disks that are part of thesame volume group must be identical. The VGDA internal architecture andChapter 6. Disk storage management 213location on the disk depends on the type of the volume group (original, big, orscalable). The volume group status area (VGSA) is used to describe the state of allphysical partitions from all physical volumes within a volume group. TheVGSA indicates if a physical partition contains accurate or stale information.VGSA is used for monitoring and maintained data copies synchronization.The VGSA is essentially a bitmap and its architecture and location on the diskdepends on the type of the volume group. A logical volume control block (LVCB) contains important information aboutthe logical volume, such as the number of the logical partitions or diskallocation policy. Its architecture and location on the disk depends on the typeof the volume group it belongs to. For standard volume groups, the LVCBresides on the first block of user data within the LV. For big volume groups,there is additional LVCB information in VGDA on the disk. For scalable volumegroups, all relevant logical volume control information is kept in the VGDA aspart of the LVCB information area and the LV entry area.

Specifying the default gateway on a specific interfaceWhen you're using HACMP, you usually have multiple network adapters installed and thus multiple network interface to handle with. If AIX configured the default gateway on a wrong interface (like on your management interface instead of the boot interface), you might want to change this, so network traffic isn't sent over the management interface. Here's how you can do this: First, stop HACMP or do a take-over of the resource groups to another node; this will avoid any problems with applications when you start fiddling with the network configuration. Then open up a virtual terminal window to the host on your HMC. Otherwise you would loose the connection, as soon as you drop the current default gateway. Now you need to determine where your current default gateway is configured. You can do this by typing: lsattr -El inet0 and netstat -nr. The lsattr command will show you the current default gateway route and the netstat command will show you the interface it is configured on. You can also check the ODM: odmget -q"attribute=route" CuAt.Now, delete the default gateway like this:lsattr -El inet0 awk '$2 ~ /hopcount/ { print $2 }' read GWchdev -l inet0 -a delroute=${GW}If you would now use the route command to specifiy the default gateway on a specific interface, like this:route add 0 [ip address of default gateway: xxx.xxx.xxx.254] -if enXYou will have a working entry for the default gateway. But... the route command does not change anything in the ODM. As soon as your system reboots; the default gateway is gone again. Not a good idea.A better solution is to use the chdev command:chdev -l inet0 -a addroute=net,-hopcount,0,,0,[ip address of default gateway]This will set the default gateway to the first interface available.To specify the interface use:chdev -l inet0 -a addroute=net,-hopcount,0,if,enX,,0,[ip address of default gateway]Substitute the correct interface for enX in the command above.If you previously used the route add command, and after that you use chdev to enter the default gateway, then this will fail. You have to delete it first by using route delete 0, and then give the chdev command. Afterwards, check with lsattr -El inet0 and odmget -q"attribute=route" CuAt if the new default gateway is properly configured. And ofcourse, try to ping the IP address of the default gateway and some outside address. Now reboot your system and check if the default gateway remains configured on the correct interface. And startup HACMP again!

Useful HACMP commandsclstat - show cluster state and substate; needs clinfo. cldump - SNMP-based tool to show cluster state cldisp - similar to cldump, perl script to show cluster state. cltopinfo - list the local view of the cluster topology. clshowsrv -a - list the local view of the cluster subsystems. clfindres (-s) - locate the resource groups and display status. clRGinfo -v - locate the resource groups and display status. clcycle - rotate some of the log files. cl_ping - a cluster ping program with more arguments. clrsh - cluster rsh program that take cluster node names as argument. clgetactivenodes - which nodes are active? get_local_nodename - what is the name of the local node? clconfig - check the HACMP ODM. clRGmove - online/offline or move resource groups. cldare - sync/fix the cluster. cllsgrp - list the resource groups. clsnapshotinfo - create a large snapshot of the hacmp configuration. cllscf - list the network configuration of an hacmp cluster. clshowres - show the resource group configuration. cllsif - show network interface information. cllsres - show short resource group information. lssrc -ls clstrmgrES - list the cluster manager state. lssrc -ls topsvcs - show heartbeat information. cllsnode - list a node centric overview of the hacmp configuration.

Hacmp can be configured in 3 ways.1. Rotating2. Cascading3. Mutual FailoverThe cascading and rotating resource groups are the “classic”, pre-HA 5.1 types. The new “custom” type of resource group has been introduced in HA 5.1 onwards.Cascading resource group:Upon node failure, a cascading resource group falls over to the available node with the next priority in the node priority list.Upon node reintegration into the cluster, a cascading resource group falls back to its home node by default.Cascading without fallback Thisoption, this means whenever a primary node fails, the package will failover to the next available node in the list and when the primary node comes online then the package will not fallback automatically. We need to move package to its home node at a convenient time.Rotating resource group:This is almost similar to Cascading without fallback, whenever package failover to the standby nodes it will never fallback to the primary node automatically, we need to move it manually at our convenience.Mutual takeover:Mutual takeover option, which means both the nodes in this type are active-active mode. Whenever fail over happens the package on the failed node will move to the other active node and will run with already existing package. Once the failed node comes online we can move the package manually to that node.

Authorization/authentication administration ____Report all password inconsistencies and not fix them: pwdck –n ALL ____Report all password inconsistencies and fix them: pwdck –y ALL ____Report all group inconsistencies and not fix them: grpck –n ALL ____Report all group inconsistencies and fix them: grpck –y ALL ____Browse the /etc/shadow, etc/password and /etc/group file weekly SUID/SGID ____Review all SUID/SGID programs owned by root, daemon, and bin. ____Review all SETUID programs: find / -perm -1000 –print ____Review all SETGID programs: find / -perm -2000 –print ____Review all sticky bit programs: find / -perm -3000 –print ____Set user .profile in /etc/security/.profile Permissions structures ____System directories should have 755 permissions at a minimum ____Root system directories should be owned by root ____Use the sticky bit on the /tmp and /usr/tmp directories. ____Run checksum (md5) against all /bin, /usr/bin, /dev and /usr/sbin files. ____Check device file permissions: ____disk, storage, tape, network (should be 600) owned by root. ____tty devices (should be 622) owned by root. ____/dev/null should be 777. ____List all hidden files in there directories ( the .files). ____List all writable directories (use the find command). ____$HOME directories should be 710 ____$HOME .profile or .login files should be 600 or 640. ____Look for un-owned files on the server: find / -nouser –print. Note: Do not remove any /dev files. ____Do not use r-type commands: rsh, rlogin, rcp and tftp or .netrc or .rhosts files. ____Change /etc/host file permissions to 660 and review its contents weekly. ____Check for both tcp/udp failed connections to the servers: netstat –p tcp; netstat –p udp. ____Verify contents of /etc/exports (NFS export file). ____If using ftp, make this change to the /etc/inetd.conf file to enable logging. ftp stream tcp6 nowait root /usr/sbin/ftpd ftpd –l ____Set NFS mounts to –ro (read only) and only to the hosts that they are needed. ____Consider using extended ACL's (please review the tcb man page). ____Before making network connection collect a full system file listing and store it off-line: ls -Ra -la>/tmp/allfiles.system ____Make use of the strings command to check on files: strings /etc/hosts grep Kashmir Recommendations Remove unnecessary services By default the Unix operating system gives us 1024 services to connect to, we want to parse this down to a more manageable value. There are 2 files in particular that we want to parse. The first is the /etc/services file itself. A good starting point is to eliminate all unneeded services and add services as you need them. Below is a screenshot of an existing ntp server etc/services file on one of my lab servers. # # Network services, Internet style # ssh 22/udp ssh 22/tcp mail auth 113/tcp authentication sftp 115/tcp ntp 123/tcp # Network Time Protocol ntp 123/udp # Network Time Protocol # # UNIX specific services # login 513/tcp shell 514/tcp cmd # no passwords used Parse /etc/rc.tcpip file This file starts the daemons that we will be using for the tcp/ip stack on AIX servers. By default the file will start the sendmail, snmp and other daemons. We want to parse this to reflect what functionality we need this server for. Here is the example for my ntp server. # Start up the daemons # echo "Starting tcpip daemons:" trap 'echo "Finished starting tcpip daemons."' 0 # Start up syslog daemon (for error and event logging) start /usr/sbin/syslogd "$src_running" # Start up Portmapper start /usr/sbin/portmap "$src_running" # Start up socket-based daemons start /usr/sbin/inetd "$src_running" # Start up Network Time Protocol (NTP) daemon start /usr/sbin/xntpd "$src_running" This helps also to better understand what processes are running on the server. Remove unauthorized /etc/inittab entries Be aware of what is in the /etc/inittab file on the AIX servers. This file works like the registry in a Microsoft environment. If an intruder wants to hide an automated script, he would want it launched here or in the cron file. Monitor this file closely. Parse /etc/inetd.conf file This is the AIX system file that starts system services, like telnet, ftp, etc. We also want to closely watch this file to see if there are any services that have been enabled without authorization. If you are using ssh for example this is what the inetd.con file should look like. Because we are using other internet connections, this file is not used in my environment and should not be of use to you. This is why ssh should be used for all administrative connections into the environment. It provides an encrypted tunnel so connection traffic is secure. In the case of telnet, it is very trivial to sniff the UID and password. ## protocol. "tcp" and "udp" are interpreted as IPv4. ## ## service socket protocol wait/ user server server program ## name type nowait program arguments ## Edit /etc/rc.net This is network configuration file used by AIX. This is the file you use to set your default network route along your no (for network options) attributes. Because the servers will not be used as routers to forward traffic and we do not want to use loose source routing at you, we will be making a few changes in this file. A lot of them are to protect from DOS and DDOS attacks from the internet. Also protects from ACK and SYN attacks on the internal network. ################################################################## ################################################################## # Changes made on 06/07/02 to tighten up socket states on this # server. ################################################################## if [ -f /usr/sbin/no ] ; then /usr/sbin/no -o udp_pmtu_discover=0 # stops autodiscovery of MTU /usr/sbin/no -o tcp_pmtu_discover=0 # on the network interface /usr/sbin/no -o clean_partial_conns=1 # clears incomplete 3-way conn. /usr/sbin/no -o bcastping=0 # protects against smurf icmp attacks /usr/sbin/no -o directed_broadcast=0 # stops packets to broadcast add. /usr/sbin/no -o ipignoreredirects=1 # prevents loose /usr/sbin/no -o ipsendredirects=0 # source routing /usr/sbin/no -o ipsrcrouterecv=0 # attacks on /usr/sbin/no -o ipsrcrouteforward=0 # our network /usr/sbin/no -o ip6srcrouteforward=0 # from using indirect /usr/sbin/no -o icmpaddressmask=0 # dynamic routes /usr/sbin/no -o nonlocsrcroute=0 # to attack us from /usr/sbin/no -o ipforwarding=0 # Stops server from acting like a router fi Securing root Change the /etc/motd banner This computer system is the private property of XYZ Insurance. It is for authorized use only. All users (authorized or non-authorized) have no explicit or implicit expectations of privacy. Any or all users of this system and all the files on this system may be intercepted, monitored, recorded, copied, audited, inspected and disclosed to XYZ Insurance's management personnel. By using this system, the end user consents to such interception, monitoring, recording, copying, auditing, inspection and disclosure at the discretion of such personnel. Unauthorized or improper use of this system may result in civil and/or criminal penalities and administrative or disciplinary action, as deemed appropriate by said actions. By continuing to use this system, the individual indicates his/her awareness of and consent to these terms and conditions of use. LOG OFF IMMEDIATELY if you do not agree to the provisions stated in this warning banner. Modify /etc/security/user root: loginretries = 5 – failed retries until account locks rlogin = false – Disables remote herald access to a root shell. Need to su from another UID. admgroups = system minage = 0 – minimum aging is no time value maxage = 4 – maximum aging is set to 30 days or 4 weeks umask = 22 Tighten up /etc/security/limits This is an attribute that should be changed due to a runaway resource hog. This orphaned process can grow to use an exorbinate amount of disk space. To provent this we can set the ulimit value here. default: #fsize = 2097151 fsize = 8388604 – sets the soft file block size to a max of 8 Gig. Variable changes in /etc/profile Set the $TMOUT variable in /etc/profile. This will cause an open shell to close after 15 minutes of inactivity. It works in conjunction with the screensaver, to prevent an open session to be used to either delete the server or worse corrupt data on the server. # Automatic logout, include in export line if uncommented TMOUT=900 4.6.5 Sudo is your friend…. This is a nice piece of code that the system administrators can use in order to allow "root-like" functionality. It allows a non-root user to run system binaries or commands. The /etc/sudoers file is used to configure exactly what the user can do. The service is configured and running on ufxcpidev. The developers are running a script called changeperms in order to tag there .ear files with there own ownership attributes. First we setup sudo to allow root-like or superuser doer access to sxnair. # sudoers file. # # This file MUST be edited with the 'visudo' command as root. # # See the sudoers man page for the details on how to write a sudoers file. # # Host alias specification # User alias specification # Cmnd alias specification # User privilege specification root ALL=(ALL) ALL sxnair,jblade,vnaidu ufxcpidev=/bin/chown * /usr/WebSphere/AppServer/installedApps/* # # # Override the built in default settings Defaults syslog=auth Defaults logfile=/var/log/sudo.log For more details, please see the XYZ Company Insurance Work Report that I compiled, or visit this URL: http://www.courtesan.com/sudo/. Tighten user/group attributes Change /etc/security/user These are some of the changes to the /etc/security/user file that will promote a more heightened configuration of default user attributes at your company. default: umask = 077 – defines umask values – 22 is readable only for that UID pwdwarntime = 7 – days of password expiration warnings loginretries = 5 – failed login attempts before account is locked histexpire = 52 – defines how long a password cannot be re-used histsize = 20 – defines how many previous passwords the system remembers minage = 2 – minimum number of weeks a password is valid maxage = 8 – maximum number of weeks a password is valid maxexpired = 4 – maximum time in weeks a password can be changed after it exp

AIX Security Checklist AIX Environment Procedures The best way to approach this portion of the checklist is to do a comprehensive physical inventory of the servers. Serial numbers and physical location would be sufficient. ____Record server serial numbers ____Physical location of the servers Next we want to gather a rather comprehensive list of both the AIX and pseries inventories. By running these next 4 scripts we can gather the information for analyze. ____Run these 4 scripts: sysinfo, tcpchk, nfsck and nethwchk. (See Appendix A for scripts) ____sysinfo: ____Determine active logical volume groups on the servers: lsvg -o ____List physical volumes in each volume group: lsvg –p "vgname" ____List logical volumes for each volume group: lsvg –l "vgname" ____List physical volumes information for each hard disk ____lspv hdiskx ____lspv –p hdiskx ____lspv –l hdiskx ____List server software inventory: lslpp -L ____List server software history: lslpp –h ____List all hardware attached to the server: lsdev –C sort –d ____List system name, nodename, LAN network number, AIX release, AIX version and machine ID: uname –x ____List all system resources on the server: lssrc –a ____List inetd services: lssrc –t 'service name' –p 'process id' ____List all host entries on the servers: hostent -S ____Name all nameservers the servers have access to: namerslv –Is ____Show status of all configured interfaces on the server: netstat –i ____Show network addresses and routing tables: netstat –nr ____Show interface settings: ifconfig ____Check user and group system variables ____Check users: usrck –t ALL ____Check groups: grpck –t ALL ____Run tcbck to verify if it is enabled: tcbck ____Examine the AIX failed logins: who –s /etc/security/failedlogin ____Examine the AIX user log: who /var/adm/wtmp ____Examine the processes from users logged into the servers: who –p /var/adm/wtmp ____List all user attributes: lsuser ALL sort –d ____List all group attributes: lsgroup ALL ____tcpchk: ____Confirm the tcp subsystem installed: lslpp –l grep bos.net ____Determine if it is running: lssrc –g tcpip ____Search for .rhosts and .netrc files: find / -name .rhosts -print ; find / -name .netrc –print ____Checks for rsh functionality on host: cat /etc/hosts.equiv ____Checks for remote printing capability: cat /etc/hosts.lpd grep v # ____nfschk: ____Verify NFS is installed: lslpp -L bin/grep nfs ____Check NFS/NIS status: lssrc -g nfs bin/grep active ____Checks to see if it is an NFS server and what directories are exported: cat /etc/xtab ____Show hosts that export NFS directories: showmount ____Show what directories are exported: showmount –e ____nethwchk ____Show network interfaces that are connected: lsdev –Cc if ____Display active connection on boot: odmget -q value=up CuAt grep namecut -c10-12 ___Show all interface status: ifconfig ALL Root level access ____Limit users who can su to another UID: lsuser –f ALL ____Audit the sulog: cat /var/adm/sulog ____Verify /etc/profile does not include current directory ____Lock down cron access ____To allow root only: rm –i /var/adm/cron/cron.deny and rm –I /var/adm/cron/cron.allow ____To allow all users: touch cron.allow (if file does not already exist) ____To allow a user access: touch /var/adm/cron/cron.allow then echo "UID">/var/adm/cron/cron.allow ____To deny a user access: touch /var/adm/cron/cron.deny then echo "UID">/var/adm/cron/cron.deny ____Disable direct herald root access: add rlogin=false to root in /etc/security/user file or through smit ____Limit the $PATH variable in /etc/environment. Use the users .profile instead.

As stated above, each network defined to HACMP should have at least two adapters per node. While it ispossible to build a cluster with fewer, the reaction to adapter failures is more severe: the resource groupmust be moved to another node. AIX provides support for Etherchannel, a facility that can used to aggregateadapters (increase bandwidth) and provide network resilience. Etherchannel is particularly useful forfast responses to adapter / switch failures. This must be set up with some care in an HACMP cluster.When done properly, this provides the highest level of availability against adapter failure. Refer to the IBMtechdocs website: http://www-03.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/TD101785 for furtherdetails.Many System p TM servers contain built-in Ethernet adapters. If the nodes are physically close together, itis possible to use the built-in Ethernet adapters on two nodes and a "cross-over" Ethernet cable (sometimesreferred to as a "data transfer" cable) to build an inexpensive Ethernet network between two nodes forheart beating. Note that this is not a substitute for a non-IP network.Some adapters provide multiple ports. One port on such an adapter should not be used to back up anotherport on that adapter, since the adapter card itself is a common point of failure. The same thing is trueof the built-in Ethernet adapters in most System p servers and currently available blades: the ports have acommon adapter. When the built-in Ethernet adapter can be used, best practice is to provide an additionaladapter in the node, with the two backing up each other.Be aware of network detection settings for the cluster and consider tuning these values. In HACMP terms,these are referred to as NIM values. There are four settings per network type which can be used : slow,normal, fast and custom. With the default setting of normal for a standard Ethernet network, the networkfailure detection time would be approximately 20 seconds. With todays switched network technology thisis a large amount of time. By switching to a fast setting the detection time would be reduced by 50% (10seconds) which in most cases would be more acceptable. Be careful however, when using custom settings,as setting these values too low can cause false takeovers to occur. These settings can be viewed using a varietyof techniques including : lssrc –ls topsvcs command (from a node which is active) or odmgetHACMPnim grep –p ether and smitty hacmp.ApplicationsThe most important part of making an application run well in an HACMP cluster is understanding theapplication's requirements. This is particularly important when designing the Resource Group policy behaviorand dependencies. For high availability to be achieved, the application must have the ability tostop and start cleanly and not explicitly prompt for interactive input. Some applications tend to bond to aparticular OS characteristic such as a uname, serial number or IP address. In most situations, these problemscan be overcome. The vast majority of commercial software products which run under AIX are wellsuited to be clustered with HACMP.Application Data LocationWhere should application binaries and configuration data reside? There are many arguments to this discussion.Generally, keep all the application binaries and data were possible on the shared disk, as it is easyto forget to update it on all cluster nodes when it changes. This can prevent the application from starting orworking correctly, when it is run on a backup node. However, the correct answer is not fixed. Many applicationvendors have suggestions on how to set up the applications in a cluster, but these are recommendations.Just when it seems to be clear cut as to how to implement an application, someone thinks of a newset of circumstances. Here are some rules of thumb:If the application is packaged in LPP format, it is usually installed on the local file systems in rootvg. Thisbehavior can be overcome, by bffcreate’ing the packages to disk and restoring them with the preview option.This action will show the install paths, then symbolic links can be created prior to install which pointto the shared storage area. If the application is to be used on multiple nodes with different data or configuration,then the application and configuration data would probably be on local disks and the data sets onshared disk with application scripts altering the configuration files during fallover. Also, remember theHACMP File Collections facility can be used to keep the relevant configuration files in sync across the cluster.This is particularly useful for applications which are installed locally.Start/Stop ScriptsApplication start scripts should not assume the status of the environment. Intelligent programming shouldcorrect any irregular conditions that may occur. The cluster manager spawns theses scripts off in a separatejob in the background and carries on processing. Some things a start script should do are: First, check that the application is not currently running! This is especially crucial for v5.4 users asresource groups can be placed into an unmanaged state (forced down action, in previous versions).Using the default startup options, HACMP will rerun the application start script which may causeproblems if the application is actually running. A simple and effective solution is to check the stateof the application on startup. If the application is found to be running just simply end the start scriptwith exit 0.Verify the environment. Are all the disks, file systems, and IP labels available?If different commands are to be run on different nodes, store the executing HOSTNAME to variable.Check the state of the data. Does it require recovery? Always assume the data is in an unknown statesince the conditions that occurred to cause the takeover cannot be assumed.Are there prerequisite services that must be running? Is it feasible to start all prerequisite servicesfrom within the start script? Is there an inter-resource group dependency or resource group sequencingthat can guarantee the previous resource group has started correctly? HACMP v5.2 and later hasfacilities to implement checks on resource group dependencies including collocation rules inHACMP v5.3.Finally, when the environment looks right, start the application. If the environment is not correct anderror recovery procedures cannot fix the problem, ensure there are adequate alerts (email, SMS,SMTP traps etc) sent out via the network to the appropriate support administrators.Stop scripts are different from start scripts in that most applications have a documented start-up routineand not necessarily a stop routine. The assumption is once the application is started why stop it? Relyingon a failure of a node to stop an application will be effective, but to use some of the more advanced featuresof HACMP the requirement exists to stop an application cleanly. Some of the issues to avoid are:Be sure to terminate any child or spawned processes that may be using the disk resources. Considerimplementing child resource groups.Verify that the application is stopped to the point that the file system is free to be unmounted. Thefuser command may be used to verify that the file system is free.In some cases it may be necessary to double check that the application vendor’s stop script did actuallystop all the processes, and occasionally it may be necessary to forcibly terminate some processes.Clearly the goal is to return the machine to the state it was in before the application start script was run.Failure to exit the stop script with a zero return code as this will stop cluster processing. * Note: This is not the case with start scripts!Remember, most vendor stop/starts scripts are not designed to be cluster proof! A useful tip is to have stopand start script verbosely output using the same format to the /tmp/hacmp.out file. This can be achievedby including the following line in the header of the script: set -x && PS4="${0##*/}"'[$LINENO]