Which THREE of these statements about the /proc and /sys pseudo-filesystems are true?
LPIC-1 Exam 101-500, objective 101. System architecture hard
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The options
Choose 3.
Correct /proc/cpuinfo describes the processors the kernel detected, including their model and supported flags
True. /proc/cpuinfo is generated by the kernel on read and is the usual place to check core count, model name and CPU feature flags such as vmx or svm.
Correct /sys exposes the kernel device model, so device attributes and the driver bound to each device are visible as a directory tree
True. sysfs is structured by kernel objects: buses, devices, classes and modules, which is why udev and tools such as lsblk read it.
Correct Writing to files under /proc/sys changes kernel tunables on the running system
True. /proc/sys is the sysctl interface, so echoing 1 into /proc/sys/net/ipv4/ip_forward has the same effect as sysctl -w net.ipv4.ip_forward=1, until the next reboot.
Not correct /proc is an ordinary on-disk filesystem, so its contents survive a reboot
False. procfs is virtual and generated in memory by the kernel; nothing under /proc is stored on disk and nothing there persists across a reboot.
Not correct The entries under /sys/class must be created by the administrator before a device can be used
False. The kernel populates sysfs automatically as devices are registered. Administrators read those entries, and udev rules match on them, but nobody creates them by hand.
Why
Both filesystems are virtual and exist only in memory. The rough division of labour: /proc is older and process-centric plus a grab bag of system information (/proc/<pid>, /proc/meminfo, /proc/interrupts, /proc/modules) and carries the sysctl tunables in /proc/sys; /sys is the newer, strictly structured view of the kernel's device model, which is what udev is built on. Changes made by writing to either are lost at reboot unless recorded in /etc/sysctl.conf or /etc/sysctl.d.
Where this comes from
- Cited
- LPI exam objective 101.1
- What it says
- Using the /proc and /sys filesystems to determine and configure hardware and kernel settings.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 101 and space the ones you get wrong.