本文介绍了SD卡读卡器通过usb连接到树莓派的挂载和卸载的操作，以及SD卡的格式化以及查看SD卡容量的命令行操作。mount umount mkfs.vfat df

当SD卡插入到树莓派板子上的时候/dev目录下会出现sda1的设备节点，有时候会出现sdb1或者sdc1设备节点。有的Linux系统上是mmcblk*的设备节点，可能和操作系统有关，也有可能是笔者连接SD卡的方式是通过一个USB hub的tf读卡器的原因。

sudo fdisk -l

值得注意的是：在系统一直运行中的时候，第一次插上SD卡，显示的是sda1，然后插拔SD卡后变成sdb1，再次插拔SD卡后变成sdc1，继续插拔SD卡，就一直是sdc1了。这可能和树莓派的系统有关，就是只能识别3个SD卡接入。reboot系统后，发现，不管SD卡热插拔多少次显示的设备节点都是sda1，在没有插SD卡时/dev目录只有sda设备节点。所以上面出现的sdb1和sdc1 可能是随机的。

SD卡的挂载：

sudo mkdir /mnt/sdcard

sudo mount -t vfat /dev/sda1 /mnt/sdcard/

因为是Windows分区，所以是vfat文件系统格式

mount -t vfat -o iocharset=utf8 /dev/sdb1 /mnt/usb/

指定中文编码格式为UTF-8

(经过上的挂载操作后发现：挂载成功后，将SD卡拔出，sudo fdisk -l下面没有sda1了，但是dev目录下仍然有sda1，查看/mnt/sdcard目录，文件仍然存在)

SD卡的卸载：

umount -v /mnt/sdcard/

SD卡的格式化操作：

1.从Linux中卸载SD卡

sudo umount -v /mnt/sdcard/

如果没有这一步操作：在格式化的时候就会出现如下错误：

pi@raspberrypi:/mnt/sdcard $ sudo mkfs.vfat /dev/sda1

mkfs.fat 4.1 (2017-01-24)

mkfs.vfat: /dev/sda1 contains a mounted filesystem.

pi@raspberrypi:/mnt/sdcard $

2.格式化SD卡

sudo mkfs.vfat /dev/sda1

3.重新挂载SD卡

sudo mount -t vfat /dev/sda1 /mnt/sdcard/

查看SD卡的总的容量和已使用过的容量以及剩余可以使用的容量

df -h /dev/sda1

pi@raspberrypi:~ $ mount -h

Usage:

mount [-lhV]

mount -a [options]

mount [options] [--source] | [--target] mount [options] mount []

Mount a filesystem.

Options:

-a, --all mount all filesystems mentioned in fstab

-c, --no-canonicalize don't canonicalize paths

-f, --fake dry run; skip the mount(2) syscall

-F, --fork fork off for each device (use with -a)

-T, --fstab alternative file to /etc/fstab

-i, --internal-only don't call the mount.helpers

-l, --show-labels show also filesystem labels

-n, --no-mtab don't write to /etc/mtab

--options-mode what to do with options loaded from fstab

--options-source mount options source

--options-source-force

force use of options from fstab/mtab

-o, --options comma-separated list of mount options

-O, --test-opts limit the set of filesystems (use with -a)

-r, --read-only mount the filesystem read-only (same as -o ro)

-t, --types limit the set of filesystem types

--source explicitly specifies source (path, label, uuid)

--target explicitly specifies mountpoint

-v, --verbose say what is being done

-w, --rw, --read-write mount the filesystem read-write (default)

-N, --namespace perform mount in another namespace

-h, --help display this help

-V, --version display version

Source:

-L, --label synonym for LABEL=-U, --uuid synonym for UUID=LABEL=specifies device by filesystem label

UUID=specifies device by filesystem UUID

PARTLABEL=specifies device by partition label

PARTUUID=specifies device by partition UUID

specifies device by path

mountpoint for bind mounts (see --bind/rbind)

regular file for loopdev setup

Operations:

-B, --bind mount a subtree somewhere else (same as -o bind)

-M, --move move a subtree to some other place

-R, --rbind mount a subtree and all submounts somewhere else

--make-shared mark a subtree as shared

--make-slave mark a subtree as slave

--make-private mark a subtree as private

--make-unbindable mark a subtree as unbindable

--make-rshared recursively mark a whole subtree as shared

--make-rslave recursively mark a whole subtree as slave

--make-rprivate recursively mark a whole subtree as private

--make-runbindable recursively mark a whole subtree as unbindable

For more details see mount(8).

pi@raspberrypi:~ $ umount -h

Usage:

umount [-hV]

umount -a [options]

umount [options] | Unmount filesystems.

Options:

-a, --all unmount all filesystems

-A, --all-targets unmount all mountpoints for the given device in the

current namespace

-c, --no-canonicalize don't canonicalize paths

-d, --detach-loop if mounted loop device, also free this loop device

--fake dry run; skip the umount(2) syscall

-f, --force force unmount (in case of an unreachable NFS system)

-i, --internal-only don't call the umount.helpers

-n, --no-mtab don't write to /etc/mtab

-l, --lazy detach the filesystem now, clean up things later

-O, --test-opts limit the set of filesystems (use with -a)

-R, --recursive recursively unmount a target with all its children

-r, --read-only in case unmounting fails, try to remount read-only

-t, --types limit the set of filesystem types

-v, --verbose say what is being done

-q, --quiet suppress 'not mounted' error messages

-N, --namespace perform umount in another namespace

-h, --help display this help

-V, --version display version

For more details see umount(8).