NIC teaming is nothing but combining or aggregating multiple network connections in parallel. This is done to increase throughput, and to provide redundancy in case one of the links fails or Ethernet card fails. The Linux kernel comes with the bounding driver for aggregating multiple network interfaces into a single logical interface called bond0. In this tutorial, I will explain how to setup bonding under Debian Linux server to aggregate multiple Ethernet devices into a single link, to get higher data rates and link failover.
Generally service such as ssh, screen, expect, telnet etc use pty (pseudo-terminals) in master â€“ slave mode for login and other purposes. If pty setting is too low many users will not able to login to system using ssh or other commands. In this tip I will explain how to increase the maximum number of pseudo-terminals.
pty man page defines pseudo-terminal as follows:
A pseudo-terminal is a pair of virtual character devices that provide a bidirectional communication channel. One end of the channel is called the master; the other end is called the slave. The slave end of the pseudo-terminal provides an interface that behaves exactly like a classical terminal. A process that expects to be connected to a terminal, can open the slave end of a pseudo-terminal and then be driven by a program that has opened the master end. Anything that is written on the master end is provided to the process on the slave end as though it was input typed on a terminal.
List the maximum number of Pseudo-terminals
Just run the following command to list / display the maximum number of Pseudo-terminals under Linux
$ cat /proc/sys/kernel/pty/max
Increase the maximum number of Pseudo-terminals (PTY)
If you have large Linux installation such as University or ISP login service you need to increase the PTYs to allow more login sessions. Open kernel configuration file – /etc/sysctl.conf:
# vi /etc/sysctl.conf
Append following config directive (support 5120 ptys)
kernel.pty.max = 5120
Save and close the file. Reload the changes:
# sysctl -p
Verify that the new maximum number of pseudo-terminals value is changed, enter:
$ cat /proc/sys/kernel/pty/max
=> Refer to sysctl, proc, and pty man pages for more information.
A step by step guide on setting up multiple SSH keys for password less login.
Finally, today I had implemented NIC bounding (bind both NIC so that it works as a single device). Bonding is nothing but Linux kernel feature that allows to aggregate multiple like interfaces (such as eth0, eth1) into a single virtual link such as bond0. The idea is pretty simple get higher data rates and as well as link failover. The following instructions were tested on:
- RHEL v4 / 5 / 6 amd64
- CentOS v5 / 6 amd64
- Fedora Linux 13 amd64 and up.
- 2 x PCI-e Gigabit Ethernet NICs with Jumbo Frames (MTU 9000)
- Hardware RAID-10 w/ SAS 15k enterprise grade hard disks.
- Gigabit switch with Jumbo Frame
The replace command is a string-replacement utility. It changes strings in place in files or on the standard input. This command uses a finite state machine to match longer strings first. It can be used to swap strings. This command is similar to the Perl -pie syntax or sed (stream editor) command.