我想知道比如/dev/shm 是在哪个文件mount上去的

[immty]

我的/etc/fstab文件没有挂载/dev/shm等信息
我想知道比如/dev/shm 是在哪个文件mount上去的，我的/etc/fstab文件没有
以下是我的文件和系统挂载的信息，请高手指点
mount
/dev/mapper/ubuntuserver-root on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
/dev/sda1 on /boot type ext2 (rw)

mty@ubuntuserver:/$ sudo df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/ubuntuserver-root
19G 12G 6.6G 63% /
none 495M 216K 495M 1% /dev
none 500M 0 500M 0% /dev/shm
none 500M 48K 500M 1% /var/run
none 500M 0 500M 0% /var/lock
none 500M 0 500M 0% /lib/init/rw
/dev/sda1 228M 17M 199M 8% /boot

mty@ubuntuserver:/$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
/dev/mapper/ubuntuserver-root / ext4 errors=remount-ro 0 1
# /boot was on /dev/sda1 during installation
UUID=4bbce307-b2eb-411b-88ba-7e8429963d51 /boot ext2 defaults 0 2
/dev/mapper/ubuntuserver-swap_1 none swap sw 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0

[Strange]

内核自动挂的，ramfs