Re: [Bug-tar] what is the point of archiving /proc "files" if you can't extract them later?

[Paul Eggert]

積丹尼 Dan Jacobson wrote:
> Well the archive created sure has a lot of their content. od -c will
> prove it to you.

No, the archive contains only metadata, not contents. For example:

$ cd /proc/self
$ tar -cf - limits | od -c
0000000   l   i   m   i   t   s  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000140  \0  \0  \0  \0   0   0   0   0   4   4   4  \0   0   0   0   1
0000160   7   5   0  \0   0   0   0   1   7   5   0  \0   0   0   0   0
0000200   0   0   0   0   0   0   0  \0   1   3   0   0   7   5   1   3
0000220   3   1   2  \0   0   1   1   5   7   5  \0       0  \0  \0  \0
0000240  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000400  \0   u   s   t   a   r          \0   e   g   g   e   r   t  \0
0000420  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000440  \0  \0  \0  \0  \0  \0  \0  \0  \0   e   g   g   e   r   t  \0
0000460  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0024000

This contains metadata, which are something like this:

$ stat limits
  File: 'limits'
  Size: 0               Blocks: 0          IO Block: 1024   regular empty file
Device: 4h/4d   Inode: 304543      Links: 1
Access: (0444/-r--r--r--)  Uid: ( 1000/  eggert)   Gid: ( 1000/  eggert)
Access: 2016-11-05 19:34:50.841898208 -0700
Modify: 2016-11-05 19:34:50.841898208 -0700
Change: 2016-11-05 19:34:50.841898208 -0700
 Birth: -

It does not contain the contents, which are something like this:

$ cat limits
Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            8720000              unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             59772                59772                processes
Max open files            1024                 65536                files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       59772                59772                signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us