Red Hat Knowledgebase

The real limit on the number of telnet sessions depends on your system resources. The number of pty's is limited to 2048 by default and is a maximum ceiling set in the kernel. Since the number of telnet sessions is dependent on system resources, you are not guaranteed to get to 2048 sessions (pty's) if system resources are low. The number of open telnet sessions can depend on the following:

• How much memory the system has
• What users are doing in the telnet sessions
• System tunables
• Network traffic

The limit is a dynamic one based on the amount of resources including memory, max processes, max file descriptors, and other system tunables. Depending on an individual systems workload, the exact number will fluctuate.