taint
also: kernel taint, tainted kernel
A kernel state that marks the Linux kernel as running under unsupported or unreliable conditions, such as when proprietary modules are loaded or hardware errors occur. Tainting helps developers identify whether problems are caused by non-standard modifications.
When the Linux kernel detects certain unsupported or problematic conditions, it sets a "taint" flag. This marks the running kernel as tainted, indicating to developers and support teams that the system may not be in a reliable or standard state. Common causes include loading proprietary kernel modules (like NVIDIA drivers), using out-of-tree code, or encountering hardware errors.
You can check if your kernel is tainted by reading /proc/sys/kernel/tainted (a non-zero value means tainted) or by running dmesg | grep -i taint. Each taint condition is represented by a letter code; for example, 'P' indicates a proprietary module, 'O' indicates an out-of-tree module, and 'W' indicates a warning from the kernel.
Tainting is primarily a diagnostic tool. It doesn't prevent the kernel from running, but it signals to developers that if a crash or bug occurs, the cause might not be in the official kernel code. This helps separate kernel issues from problems caused by third-party or unsupported modifications.