Switch the primary group with secondary group temporarily

This command is used to switch / swap between primary group and secondary group in a session.

$ id
uid=33119(kasim) gid=33119(users) group=3333(sysadm)
$ newgrp sysadm
$ id
uid=33119(kasim) gid=3333(sysadm) group=33119(users)

Admin tools for cluster manipulation

A tool to manage and configure cluster overall:
# smitty hacmp

A tool to manage RG(s) and cluster generally:
# smitty cl_admin

A tool to start cluster:
# smitty clstart

A tool to stop cluster gracefully, fail over or force:
# smitty clstop

A command to check the cluster services:
# lssrc -g cluster

Set user ID, set group ID, sticky bit

Source taken from: http://wiki.e107.org/?title=Unix_Permissions

In addition to the basic UNIX permissions, there are also three bits of information defined for files in UNIX:

• SUID or setuid: change user ID on execution. If setuid bit is set, when the file will be executed by a user, the process will have the same rights as the owner of the file being executed.
• SGID or setgid: change group ID on execution. Same as above, but inherits rights of the group of the owner of the file. For directories it also may mean that when a new file is created in the directory it
• Sticky bit. It was used to trigger process to "stick" in memory after it is finished, now this usage is obsolete. Currently its use is system dependant and it is mostly used to suppress deletion of the files that belong to other users in the folder where you have "write" access to.

Numeric representation

Octal digit Binary value Meaning

• 0 000 setuid, setgid, sticky bits are cleared
• 1 001 sticky bit is set
• 2 010 setgid bit is set
• 3 011 setgid and sticky bits are set
• 4 100 setuid bit is set
• 5 101 setuid and sticky bits are set
• 6 110 setuid and setgid bits are set
• 7 111 setuid, setgid, sticky bits are set

Textual representation

SUID

• If set, then replaces "x" in the owner permissions to "s", if owner has execute permissions, or to "S" otherwise. Examples:
• -rws------ both owner execute and SUID are set
• -r-S------ SUID is set, but owner execute is not set

SGID

• If set, then replaces "x" in the group permissions to "s", if group has execute permissions, or to "S" otherwise. Examples:
• -rwxrws--- both group execute and SGID are set
• -rwxr-S--- SGID is set, but group execute is not set

Sticky

• If set, then replaces "x" in the others permissions to "t", if others have execute permissions, or to "T" otherwise. Examples:
• -rwxrwxrwt both others execute and sticky bit are set
• -rwxrwxr-T sticky bit is set, but others execute is not set

What are the SUID, SGID and the Sticky Bits?

Source taken from http://www.codecoffee.com/tipsforlinux/articles/028.html

Linux has some special attributes associated with all files. Often in X Windows when you check the properties of any file (by right clicking on it and viewing its properties) you would get to see 3 special attributes besides the common read/write/execute rights for the owner/group/others. The 3 extra attributes are known as SUID, SGID and Sticky Bits

Sticky Bit

Lets start with Sticky bit first. Since this is the most simplest to explain. Setting the sticky bit tells Unix that once the concerned application is executed, it should remain in memory. Remember that Unix is a multi-user OS and was mainly designed so that multiple users can work simultaneously. Thus the logic used is that a program that exists in memory requires lesser time to start when a new user requests for the same program. Thus when one user has just used a program and then a new user wants to use the same program, the second user doesn't have to face a time delay for the program to initialize itself. It would be readily available to him. The concept of the sticky bit was a very useful one, long back when fast disk access and other memory access technologies weren't around. But in today's age the concept of sticky bit is obsolete, since modern day technology is advanced enough to reduce the time delay while loading applications into the memory. Thus currently the sticky bit is of very little significance. Sticky bit is only associated with executables.

SUID (Set User ID) Bit

Sometime you may faced an error while trying to run any application stating that the application must be 'SUID root' . You might have been confused that time, but now once you read this article you would no longer find it confusing.

SUID stands for Set User ID. This means that if the SUID bit is set for any application then your user ID would be set as that of the owner of application/file rather than the current user, while running that application. That means in case I have an application whose owner is ' root ' and it has its SUID bit set, then when I run this application as a normal user, that application would still run as root. Since the SUID bit tells Linux that the the User ID root is set for this application and whenever this application executes it must execute as if root was executing it (since root owns this file).

In case you have really understood the above you may be wondering - isnt this a major security risk? If users are able to run applications as root, then it must be definitely posing as a threat to the security of the system. Actually the SUID is used to increase the security in a way. Let me explain this with my own example I use on my machine.


One way I use SUID on my machine

I have a few files that I modify through Linux and then before I shutdown Linux I have to transfer them to my Windows partition for further use there. As a normal user I do not have write access to the Windows partitions that I have mounted. So I have to be the superuser to be able to write to that partition. I have created a simple shell script that copies my files to the Windows partitions. This script was created by root user and the SUID bit was set. Access rights to this script have been given to all users. Now whenever I want to copy my files I simply run this script. Even though I have logged in as a normal user, the SUID bit which is set causes this script to execute as if the root was executing it and it allows me to write to the Windows partitions.

Had the SUID bit not been set, I would have to type ' su ' at the prompt and get temporary superuser access to get write access to the Windows partitions. Hope you got the point..

You may be thinking that since these applications would run as root they can do harmful things and destroy the system. The concept behind SUID bit is that you as the superuser would be able to allow certain applications / scripts to be run by the users as if they were the superuser for the time being. What these application / scripts do when they execute should be completely known to you. Even though the users would be allowed to execute these programs as root they would be able to do ONLY THOSE things that these programs were designed to do. So in case a script was designed to copy 5 files from one place to another. Then the user who would run that script would be able to ONLY copy those 5 files from one place to another. He would not be able to modify that script in any way since he would not have write access to the script. He would only be having execute rights for that script. Hence its an excellent idea to allow users to do some important backup using a script that does only that and by setting the SUID bit for that script. This way the users don't have to know the superuser password but can still use some facilities that are only available to the superuser

Important : Think twice before setting the SUID bit for scripts (owned by root) that take arguments at the command line. Since you never know what parameters a malicious user may pass to your script. Since the script would run as root it could do great damage if misused.


SGID (Set Group ID) bit

Just like SUID, setting the SGID bit for a file sets your group ID to the file's group while the file is executing. IT is really useful in case you have a real multi-user setup where users access each others files. As a single homeuser I haven't really found a lot of use for SGID. But the basic concept is the same as the SUID, the files whose SGID bit are set would be used as if they belong to that group rather than to that user alone.

Note : Making SUID and SGID programs completely safe is very difficult (or maybe impossible) thus in case you are a system administrator it is best to consult some professionals before giving access rights to root owned applications by setting the SUID bit. As a home user (where you are both the normal user and the superuser) the SUID bit helps you do a lot of things easily without having to log in as the superuser every now and then.

HACMP health-check command

To check RG availability on HACMP server, execute the command as below:

# /usr/es/sbin/cluster/utilities/clRGinfo

To check setting of the HACMP cluster:

# /usr/es/sbin/cluster/utilities/cltopinfo

To check the current status of the cluster:

# /usr/es/sbin/cluster/utilities/clstat

How to collect system info for IBM to investigate (snap command)

Below is the general step how to collect system info for IBM to investigate:

1. run snap -r (answer yes if asked).
2. run snap -ac (additional option '-e' to collect HAMCP cluster information)
3. rename the file in step 2. under /tmp/ibmsupt directory to the name that has been specified by IBM themselves. xxxxxxxx.snap.pax.Z
4. upload the renamed file (step 3) to our FTP server:

ftp server: ftp.XxxXxxx.ibm.com
login: anonymous
passwd:
upload dir: /toibm/aix

Hitachi Dynamic Link Manager on AIX manipulation command

Today's work lead me to find and learn new command for managing and verifying Hitachi Disks Array on AIX machine:

Source taken from http://www.coolcommands.com/index.php?option=com_cccat&task=display&id=47

hdlm - Hitachi SAN disk correspondance Description

Correspondance for physical disks for a Hitachi SAN:

4 hdisk = 4 dlmfdrv = 1 physical disk

HDLM commands:

Command to discover all dlmfdrv:

# dlmcfgmgr

Command to verify the disks on a HITACHI SAN:

- the system:

# dlnkmgr view -sys

- the drivers

# dlnkmgr view -drv

- the paths

# dlnkmgr view -path

Changing the Auto Failback feature

# dlnkmgr set -afb on
dlnkmgr set -afb on
Execute command? [y/n] : y
KAPL01001-I The HDLM command completed normally. Opestartration name = set

Changing the Path Health Checking feature

# dlnkmgr set -pchk on
dlnkmgr set -pchk on
Execute command? [y/n] : y
KAPL01001-I The HDLM command completed normally. Operation name = set

To bring LUN online in the system

# dlnkmgr online -path -pathid 000001