Author Archives: TKH Specialist
Denyhosts Assists
- Apr
- 10
- Posted by TKH Specialist
- Posted in Security, System Administration
Every so often a legitimate user will get blocked by deny hosts. When this happens you can re-enable their access with these 8 simple steps (UPDATE: or use the faster version, see below): Stop DenyHosts # service denyhosts stop Remove the IP address from /etc/hosts.deny Edit /var/lib/denyhosts/hosts and remove the lines containing the IP address. […]
read moreTesting Database Connectivity
- Mar
- 31
- Posted by TKH Specialist
- Posted in databases, System Administration
Working with databases and new application installations can be really fun. Problem is, when there is a problem, everyone starts the blame game. Nothing unusual about that, part of an administrators job is to troubleshoot and prove where the problem starts. When dealing with external databases, there can be numerous problem, the firewall could be […]
read moreOCI on RHEL6
- Mar
- 31
- Posted by TKH Specialist
- Posted in redhat
Our developers had to have OCI. Now that I got that out of the way. 😉 We use Oracle as our DB for most applications (calm down, like you couldn’t have figured that out). In setting up a new application server for a custom application it came to my attention that the application used oci […]
read morePain often equals Progress
- Nov
- 07
- Posted by TKH Specialist
- Posted in redhat, System Administration, Tools
It has been one of those weeks. Not fun, to many hours worked, personal events missed, you know the kind of week I am talking about. If not…what do you do for a living?! Despite all the pain and stress this week has resulted in Progress, an increased understanding of certain products and new ways […]
read moreWhen Tomcat stops responding to Apache
- Sep
- 18
- Posted by TKH Specialist
- Posted in apache, Kuali, tomcat
Today our multi-node tomcat servers became unresponsive to user/web traffic. A quick look at our monitoring tools indicated that the tomcat servers were running healthily. While the application administrator looked at catalina.out to see if we were missing something, I dug into the load balancer logs. I immediately saw the following errors: [Date] [error] ajp_read_header: […]
read moreSSH – weak ciphers and mac algorithms
- Jun
- 25
- Posted by TKH Specialist
- Posted in System Administration, Tools
A security scan turned up two SSH vulnerabilities: SSH Server CBC Mode Ciphers Enabled SSH Weak MAC Algorithms Enabled To correct this problem I changed the /etc/sshd_config file to: # default is aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, # aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, # aes256-cbc,arcfour # you can removed the cbc ciphers by adding the line Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,arcfour # default is hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 # […]
read moreCacti, RRDs, and Disk Block Sizes
- May
- 13
- Posted by TKH Specialist
- Posted in linux
Abstract Disk block size on Linux for the ext2/3/4 file system does not affect the amount of data written to disk. Apparently, all of the allowed values for blocksize (1024, 2048 or the default of 4096 bytes) result in data … Continue reading →
read moreThe Root of Missing Mail
- Apr
- 30
- Posted by TKH Specialist
- Posted in redhat, System Administration
Like all conscientious system administrator I like to keep tabs on my servers. One way of doing this is checking root’s email daily. This is a great idea if you have a few servers and never take vacation! I manage close to 100 servers, so I need a more efficient way of “hearing” my servers […]
read moreRecursive Gzip Sometimes Helps
- Apr
- 16
- Posted by TKH Specialist
- Posted in linux
Everyone knows that gzip’ing a file will usually make it smaller, but gzip’ing it again will not. In other words, once you’ve compressed a file, it won’t compress further. But here’s an exception. If you make a file of … Continue reading →
read moreTroubleshooting C and C++ compilation
- Mar
- 29
- Posted by TKH Specialist
- Posted in Programming
Here’s a list of cryptic compiler messages and what I think they are trying to tell you GPU_MD.h(12): here is inaccessible Your C++ class constructor is defined as private in the Class header. Don’t forget to use the public keyword to make your constructor public.
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