CloudLinux monitoring and limits
This article discusses how CloudLinux monitors and regulates resource usage on shared and reseller hosting servers to improve performance and stability.
Shared and reseller servers run CloudLinux, an operating system that includes many features for optimizing shared hosting environments. Because shared and reseller servers host many accounts, an account using too many resources can lead to problems on the entire server.
CloudLinux helps prevent these types of problems by actively monitoring resource usage, and proactively limiting accounts when they exceed predefined resource usage limits.
CloudLinux checks running processes every minute. Because CloudLinux does not check processes every second, it is possible that short intervals of high usage can be missed.
What CloudLinux monitors and regulates
CloudLinux monitors and regulates the following system resources:
- CPU usage: If your account's CPU usage exceeds predefined limits, CloudLinux slows it down to acceptable limits. Your site remains available during this time. When CPU usage falls below the maximum limit, CloudLinux stops limiting your site. DDoS (Distributed Denial of Service), spambot, and brute force attacks are all possible causes of high CPU usage. A poorly configured site can also cause this limit to be reached.
To determine your account's current CPU usage, log in to cPanel. On the cPanel home screen, under Stats, locate CPU Usage.
- Input/output (disk) usage: If disk usage exceeds predefined limits, CloudLinux slows down your site to bring it back within acceptable limits. Your site remains available during this time.
- Memory usage: CloudLinux monitors your account's virtual and physical memory usage. If memory usage exceeds predefined limits, visitors to your site receive “500 Internal Server Error” or “503 Error” messages in their web browser. Additionally, CloudLinux slows down your site to bring it back within acceptable limits.
To determine your account's current memory usage, log in to cPanel. On the cPanel home screen, under Stats, locate Virtual Memory Usage and Physical Memory Usage. Please note that the Physical Memory Usage value also includes disk cache usage, so the actual amount of physical memory usage is not entirely accurate. If the actual amount of available physical memory ever runs low, however, CloudLinux automatically frees the disk cache memory.
- Process usage: CloudLinux monitors the number of processes running on your account. HTTP, SSH, CGI, and PHP connection requests all count towards this predefined limit, which is generous. If your web site exceeds this limit, visitors receive “503 Error” messages in their web browser. The limit is primarily in place to help prevent DDoS, spambot, and brute force attacks from affecting entire servers. However, a poorly configured site can also cause this limit to be reached.
To determine your account's current process usage, log in to cPanel. On the cPanel home screen, under Stats, locate Entry Processes.
- MySQL usage: CloudLinux's MySQL Governor monitors your account's MySQL usage and restricts it if any of the following resources exceed predefined limits:
- CPU usage
- Disk reads and writes
- Number of database connections
No error messages are displayed when this restriction occurs. When MySQL usage falls below the predefined limits, the MySQL Governor removes the restrictions. DDoS (Distributed Denial of Service), spambot, and brute force attacks, as well as plugins and unoptimized databases, are all possible causes of high MySQL usage.
A2 Hosting's Smart System Notifier also monitors server performance and stability. Instead of monitoring usage constantly like CloudLinux, the Smart System Notifier monitors accumulated daily usage totals. For additional information about the Smart System Notifier, as well as possible causes of high system usage, please see these articles