The Acumen IT Support blog provides you with helpful articles about Linux software operating systems.
Several web sites provide good overviews.
Zabbix Problem & Solution
This occurs when you confirm that the service is running, but the frontend still won’t show server is running.
Found that turning off SELinux with setenforce 0 would fix the problem, so it is clearly SELinux related. The problem is that by default, SELinux prevents apache/php from connecting to network ports, even on localhost. To fix this, you must allow the SELinux rule: httpd_can_network_connect.
sudo setsebool httpd_can_network_connect on
sudo may not be necessary in your environment
sudo getsebool -a | grep httpd
look for httpd_can_network_connect –> on
sudo setenforce 1
This ensures that SELinux is running.
Do NOT just turn off SELinux. It is very effective at protecting your machine from attack.
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When trying to configure sftp, you encounter “fatal: safely_chroot permission denied” in your SElinux audit.log.
When you disable selinux with setenforce 0, sftp works.
When you enable selinux with setenforce 1, sftp fails and gives an error like:
Aug 7 18:01:19 server1 sshd[36015]: fatal: safely_chroot: stat(“/var/www”): Permission denied
You must have:
setsebool -P ssh_chroot_rw_homedirs=1
This will often error if you have an sftp user that also has a login shell (a big no-no), set it to /sbin/nologin with:
usermod -s /sbin/nologin mySFTPUser
But sftp still won’t work because the internal SELinux policies don’t allow sftp chroot. Create a custom SELinux policy to allow the chroot using audit2allow:
yum install setroubleshoot (to get audit2allow)
or
yum install policycoreutils-python (alternate package with audit2allow)
cd /root
grep chroot_user_t /var/log/audit/audit.log | audit2allow -M sftp_chroot_custom_policy > sftp_chroot_custom_policy.text
semodule -i sftp_chroot_custom_pol.pp
NOTE: The normal out put of this would be the .pp file generated by the -M flag. The .text file contains the human readable equivalent. You must use the .pp binary file with the semodule -i command.
This applies to Centos 6. It may apply to other Linux operating systems.
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HOWTO: Upgrading the CentOS kernel for a Hyper-V virtual machine with Linux Integration Components.
A kernel upgrade will cause a kernel panic. These instructions prevent the boot crash.
Upgrade the kernel:
#yum upgrade
If you boot with this, you will get the kernel panic. Don’t worry. Just press space at boot time and boot from your old kernel. Write down your new kernel number, such as 2.6.18-274.17.1.el5
Compile the Linux IC for your new kernel. You can use the latest IC at this time is v3.2:
mkdir /opt/linux_ic_rtm
cp -r /media/CDROM/* /opt/linux_ic_rtm
cd /opt/linux_ic_rtm
grep -ilR uname * | xargs sed -i 's/uname -r/echo "2.6.18-274.17.1.el5"/g'
make && make install
reboot
You can now let grub boot to your default kernel without a kernel panic.
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