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Disable first time password change in AIX
How to disable first time password change in AIX? Usually in AIX, if you change the password of a user, it will prompt the user to change his password when he login first time. To disable this first time password change in AIX Server, Clear the ADMCHG flag of the user account. pwdadm -c <USER_NAME> Example: #pwdadm –c testuser1 Open Files – Linux
ope it will be useful to you as well..
You might have this scenario; Logfiles deleted while the process is still running. That’s annoying: On your Linux-Server the /var filesystem is nearly full. You remove a very large logfile that you don’t need with the rm command:
myserver1# df -Ph /var
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/root-var 7.1G 7.0G 100M 99% /var
myserver1# ls -l /var/log/myapp/userlog
myserver1# rm /var/log/myapp/userlog
myserver1# df -Ph /var
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/root-var 7.1G 7.0G 100M 99% /var
But what’s that? The filesystem is still full. With lsof you can see, that the logfile is still opened in write mode:
myserver1# lsof | grep var/log/myapp/userlog
To actually free up the space you would have to stop the logging process. But since this might be a mission critical application this is not always an option. Is there any way to get rid of the file without stopping the logging process?
Find the deleted file’s representation under /proc
Actually we cannot remove the file as long as the file is still in use by a process. But what we can do is: Getting the size down to 0. Thanks to Linux’ enhanced /proc filesystem.
And that’s how you do it:
First find the process that still uses the file (we already did that – see above):
myserver1# lsof | grep var/log/myapp/userlog
myapp 25139 root 4w REG 3,12 0 2101404 /var/log/myapp/userlog (deleted)
lsof tells us that a process with PID=25139 has opened the file (with number 4) in write mode. See the bolded part of the lsof output.
Knowing the PID of the process and the file number we can visit its representation under /proc:
myserver1# cd /proc/25139/fd
myserver1:/proc/25139/fd# ls -l 4
lr-x—— 1 root root 64 2010-01-07 17:10 4 -> /var/log/myapp/userlog (deleted)
We can do almost everything with this file (called 4 here) what we can do with a real file: we can less it, copy it, and we can change its contents!
Free up the Space
As already said, we cannot remove the file, but what we can do is getting the size down to zero. And that’s done as with every other file, e.g. if you use bash (or ksh) – what is most likely under Linux:
myserver1# > /proc/25139/fd/4
myserver1# df -Ph /var
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/root-var 7.1G 4.9G 1.2G 69% /var
As we see there is again free space under /var, and the process is still running:
myserver1# lsof | grep var/log/myapp/userlog
myapp 25139 root 4w REG 3,12 0 0 /var/log/myapp/userlog (deleted)
What more could be done…?
As said before you can work on this file as you work on real files. That means, you could even save this file and compress it before getting its size down to 0:
myserver1# cp /proc/25139/fd/4 /tmp/userlog
myserver1# gzip -9 /tmp/userlog
myserver1# mv /tmp/userlog.gz /var/log/myapp/userlog.1.gz
myserver1# > /proc/25139/fd/4
Final Remarks
This procedure helps you if you are in a pinch – but basically you should never remove such an open file, because you still have an issue here: The process still writes to this file – and the only way to see what it logs is to use the procedure to save the file as shown above.
So remember to bring the size down to 0 in the first place instead:
myserver1# > /var/log/myapp/userlog
This way the space in the filesystem is freed immediately – and you still see what your application is writing to this file.
Configuring TCP Wrappers
The TCP Wrappers package is installed by default on Fedora Linux and provides host-based security separate from that provided by a firewall running on the server itself or elsewhere. /etc/hosts.allow: Defines the hosts and networks allowed to connect to the server. The TCP Wrappers enabled application searches this file for a matching entry, and if it finds one, then the connection is allowed. /etc/hosts.deny: Defines the hosts and networks prohibited from connecting to the server. If a match is found in this file, the connection is denied. No match means the connection proceeds normally. The /etc/hosts.allow file is always read first and both files are always read from top to bottom, therefore the ordering of the entries is important. <TCP-daemon-name> <client-list> : <option> # # Determining the TCP Daemon’s Name: [root@mysrv1 tmp]# ps -ef | grep -i ssh For a full explanation of all the options available, refer to section 5 of the man pages for hosts_access: [root@mysrv1 tmp]# man 5 hosts_access TCP Wrappers is simple to implement, but you have to set them on every host. Management is usually easier on a firewall that protects the entire network. AIX Boot Process
AIX Booting Process explained below. Phases of the Boot Process: 1. Read Only Storage Kernel Init Phase 1. Motherboard is Checked 2. Base Device Configuration Phase 3. System Boot Phase Changing boot order in AIX What does the boot logical volume(blv) contains? Contents of Boot Logical Volume in AIX
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| No 1 2 3 4 |
Source 11:22:33:44:55:66 11:22:33:44:11:11 11:22:33:44:11:11 11:22:33:44:55:66 |
Destination 11:22:33:44:11:11 11:22:33:44:55:66 11:22:33:44:55:66 11:22:33:44:11:11 |
Prot ARP ARP ARP ARP |
Info who has 192.168.1.1? Tell 192.168.1.2 192.168.1.1 is at 11:22:33:44:11:11 who has 192.168.1.2? Tell 192.168.1.1 192.168.1.2 is at 11:22:33:44:55:66 |
ARP TRAFFIC after the poisoning
The router ARP broadcast request is answered by the Windows machine similarly than in the previous capture.
The difference between the two steps comes from the fact that there is no request coming from Windows (192.168.1.2) to find the MAC address associated to the router (192.168.1.1) because the poisoner continuously sends ARP packets telling the Windows machine that 192.168.1.1 is associated to his own MAC address (11:22:33:44:99:99) instead of the router MAC address (11:22:33:44:11:11).
| No 1 2 3 4 |
Source 11:22:33:44:11:11 11:22:33:44:55:66 11:22:33:44:99:99 11:22:33:44:99:99 |
Destination 11:22:33:44:55:66 11:22:33:44:11:11 11:22:33:44:55:66 11:22:33:44:55:66 |
Prot ARP ARP ARP ARP |
Info who has 192.168.1.2? Tell 192.168.1.1 192.168.1.2 is at 11:22:33:44:55:66 192.168.1.1 is at 11:22:33:44:99:99 192.168.1.1 is at 11:22:33:44:99:99 |
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