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Sunday, February 27, 2011

Bigger buffer log (dmesg) size

Someone asked me: how to make dmesg output is not truncated. The answer is make the buffer log size bigger. How? As far as I know, there are two ways to raise the buffer log size:
  1. Pass the parameter of log_buf_len=n to kernel, where n is a power of two number (n = 2^x). The default for slackware is 2^15 or 32768 (32k). You can change n to 65536 (2^16) or 131072 (2^17). In this way, you don't need to recompile your current kernel.
  2. Compile or recompile your kernel. Before you compile the kernel yourself or recompile it yourself, you have to change the kernel parameter in General Setup > Kernel log buffer size (see figure) to 16 (65536) or 17 (131072). After compilation, don't forget to copy kernel image, config, and System.map into /boot directory and set up your bootloader (lilo/grub) properly.


Choose one of them then you will get full dmesg output on your screen. It will be very long message log.

1 comment:

Anonymous said...

You can also specify log_buf_len in kilobytes, megabytes or gigabytes using the K, M or G postfix. For example log_buf_len=32K will result 32 kilobytes log buffer, log_buf_len=1M will specify 1 megabytes log buffer. See https://github.com/torvalds/linux/blob/master/Documentation/kernel-parameters.txt#L1724 for the original documentation.