title: if there is no sysfs in /etc/fstab, how sysfs is mounted?
body: <p>If I type $mount on shell, it shows several mount point</p>
  
  <pre><code>proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
  sys on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
  dev on /dev type devtmpfs (rw,nosuid,relatime,size=3030352k,nr_inodes=757588,mode=755)
  ....
  ....
  tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=606608k,mode=700,uid=1000,gid=1000)
  binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,relatime)
  </code></pre>
  
  <p>I searched web and it says i could setup mount point by editing fatab.<strong>(like sysfs /sys sysfs noauto 0 0)</strong>
  <strong>but in my /etc/fstab, there is no such description about sysfs, it only has descrption about /dev/sda1.</strong></p>
  
  <p>Then, how does my linux understand sysfs mount point? and who mounts it?</p>