Buffered file I/O can pass through a language buffer, the kernel page cache, and the storage stack at different times. Modified cache pages need writeback so their data reaches the backing filesystem and device. This separation can combine work and improve throughput, but it means that another reader seeing new bytes is not, by itself, evidence that a crash-safe storage boundary has completed. ...
Swap gives Linux a backing store for eligible memory pages that need not remain resident. It can preserve cold data while RAM serves active work, but it does not make the machine’s working set fit at RAM speed. The useful question is whether reclaim frees space without repeatedly stalling important tasks. Swap occupancy, swap traffic, and application progress answer different parts of that question. ...
When memory tightens, cold pages would go to a slow disk. zram keeps them in compressed RAM instead, trading a little CPU for much more headroom. A compressed block device in memory zram is a block device that lives in RAM and stores compressed data instead of talking to a real disk. When the kernel swaps a page into it, the page is compressed and kept in memory, so the memory gain comes from shrinking the pages rather than moving them to slow storage. Because the device is memory-backed, it answers reads and writes far faster than a disk-backed swap, but the space it provides is limited by how compressible the pages are and by how much memory you are willing to trade for the swap. ...
Signals notify processes or threads of events using kernel-defined delivery rules. A signal’s disposition selects a default action, an installed handler, or ignoring it where permitted. A thread’s mask can block delivery of eligible signals while they remain pending. Separating disposition, masking, and pending state is essential when a program appears to miss repeated notifications or fails to stop as expected. ...
On Linux, sysctl exposes selected kernel parameters through /proc/sys. It can inspect the running state, and an authorized write can change that state without rebooting. A configuration file is a separate instruction to a loader. Confusing these two layers produces a familiar incident: the desired value is on disk, but the kernel is doing something else. ...
Logrotate evaluates configuration when invoked, rotates eligible logs, and applies the selected retention and compression actions. A timer or another scheduler determines when that evaluation happens. The tool does not continuously cap file size, and renaming a log does not automatically redirect an application’s open descriptor. A working setup combines evaluation frequency, file policy, and the writer’s actual reopening behavior. ...
A schedule must specify what time means. “At nine each morning in New York” refers to a civil-time calendar. “A quarter hour after this job finishes” refers to an elapsed interval and an event. systemd timers support both, but the two clocks and reference points have different behavior around time-zone changes, suspension, and periods when the timer is inactive. ...
cgroup v2 organizes resource control in a unified hierarchy. A workload’s processes can share aggregate budgets, with limits inherited through the hierarchy rather than applied only to one particular PID. CPU bandwidth, memory usage, and task count are separate controllers with different enforcement behavior. Reading the actual cgroup files and failure counters is more useful than treating every configured limit as the same kind of hard stop. ...