After mount
there are listed some filesystems. I need to know what's in the /dev
, /proc
and /sys
. Some examples would be great!
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1Take a look at this: http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard – dgsleeps Mar 08 '15 at 14:55
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@dgsleeps the FHS doesn't define the contents of /proc and /sys because they are kernel depended – Junaga Oct 24 '16 at 00:23
1 Answers
The /dev
tree contains device nodes, which gives user space access to the device drivers in your OS's running kernel.¹ All POSIX type OSes have a /dev
tree.
The /proc
tree originated in System V Unix, where it only gave information about each running process, using a /proc/$PID/stuff
scheme. Linux greatly extended that, adding all sorts of information about the running kernel's status. In addition to these read-only information files, Linux's /proc
also has writable virtual files that can change the state of the running kernel. BSD type OSes generally do not have /proc
at all, so much of what you find under here is non-portable.
The intended solution for this mess in Linux's /proc
is /sys
. Ideally, all the non-process information that got glommed into the /proc
tree should have moved to /sys
by now, but historical inertia has kept a lot of stuff in /proc
. Often there are two ways to effect a change in the running kernel: the old /proc
way, kept for backwards compatibility, and the new /sys
way that you're supposed to be using now.²
Footnotes:
There are also several
/dev
entries that do not correspond to hardware devices, such as/dev/null
,/dev/random
, and/dev/tty
. These are virtual devices that let user space programs talk to other parts of the kernel besides the running drivers in a device-like fashion.As a rule,
/sys
tends to be more strictly organized than/proc
, since/sys
mirrors the internal kernel data structures that manage the system's resources, whereas/proc
grew organically over many years, and old questionable design decisions can't change now because there are programs using those old interfaces./sys
started out with a clearer design, and doesn't have to drag around as much historical baggage as/proc
.

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1Also, they don't keep the sort of files that you should backup. They are dynamically generated. They use special “Magic” file-systems. – ctrl-alt-delor Mar 08 '15 at 18:37