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rapt
Asked: 2022-04-03 01:25:20 +0800 CST

Why doesn't 'sudo cp' copy files in the /sys directory?

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I want to make an exact copy of the /sys directory, and tried the following command:

sudo cp -ra /sys ~/Documents/dir1

It does not work as I expected... I get a lot of error messages such as:

cp: error reading '/sys/fs/cgroup/memory/memory.force_empty': Invalid argument
cp: error reading '/sys/devices/system/cpu/cpu0/cache/index0/power/autosuspend_delay_ms': Input/output error
cp: cannot open '/sys/devices/system/clockevents/clockevent0/unbind_device' for reading: Permission denied
cp: error reading '/sys/devices/virtual/block/loop0/trace/enable': No such device or address

Why isn't sudo enough to make cp copy every file?

sudo

1 Answers

  1. Best Answer

    The /sys directory isn't a normal directory, but instead a "virtual" one. From "The Linux Filesystem Explained":

    /sys

    /sys is another virtual directory like /proc and /dev and also contains information from devices connected to your computer.

    In some cases you can also manipulate those devices. I can, for example, change the brightness of the screen of my laptop by modifying the value stored in the /sys/devices/pci0000:00/0000:00:02.0/drm/card1/card1-eDP-1/intel_backlight/brightness file (on your machine you will probably have a different file). But to do that you have to become superuser. The reason for that is, as with so many other virtual directories, messing with the contents and files in /sys can be dangerous and you can trash your system. DO NOT TOUCH until you are sure you know what you are doing.

    Similar directories are /dev, /proc and /run.

    Since files in these directories are created, changed and removed all the time while the system is running, it doesn't make any sense to copy them.

    Think more of these directories as a dynamic snapshot of the current state of the system, rather than a static medium of storage.

    The reason you get errors even with sudo is probably that the files are either fully locked or removed by the system before the cp command could take effect.

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