Dmesgrestrict

Dmesgrestrict is a term commonly used to refer to the Linux kernel parameter kernel.dmesg_restrict, which controls access to the kernel’s message buffer via the dmesg utility. The kernel maintains a ring buffer of kernel messages, which can contain information about hardware, drivers, and system state. Restricting access to this buffer is a security and privacy consideration on multi-user systems and in environments where sensitive information should not be exposed to unprivileged users.

The setting is exposed as a sysctl-like knob, typically available at /proc/sys/kernel/dmesg_restrict. In many kernel versions, a value of 0 means no restriction (unprivileged users can read the kernel log with dmesg), while a value of 1 restricts read access to privileged users (usually root) or to processes with the appropriate capabilities. Some kernels may support additional, less common values or behaviors, but 0 and 1 are the standard options. The exact effect can depend on the kernel version and distribution.

Configuration and management are performed through sysctl tools or by writing to the corresponding proc entry. For example, echoing 1 to /proc/sys/kernel/dmesg_restrict or using sysctl -w kernel.dmesg_restrict=1 sets the restriction. To make the change persistent across reboots, place a corresponding line in a sysctl configuration file, such as /etc/sysctl.d/dmesg.conf.

Security implications and usage considerations: enabling dmesgrestrict reduces the risk of leaking kernel messages to non-privileged users but may hinder debugging or automated monitoring by non-root processes. Administrators should balance security needs with operational requirements.

See also: dmesg, kernel.dmesg_restrict, /proc/sys/kernel/dmesg_restrict.