During an investigation into a file server that periodically becomes unresponsive, a Linux administrator captures a snapshot of running processes with:
ps -eo pid,stat,command | head
In the output, the STAT column for several commands shows the single-letter code D, while other processes display S, T, or Z. According to the ps manual, which of these codes identifies a task that is in an uninterruptible sleep state (typically waiting on disk or other I/O) and therefore will not respond to kill signals until the event completes?
The letter D in the STAT column means the kernel has placed the task in an uninterruptible sleep. The process is blocked waiting for a resource such as disk I/O and will ignore most signals until the request finishes. By contrast, S represents an interruptible sleep that can be awakened by a signal, Z marks a defunct (zombie) task whose parent has not yet reaped it, and T indicates a process that has been stopped (for example, by Ctrl+Z or by a debugger).
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