> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/ask/flat/chapter-25-storage-management/di-25.1-jie-usb-cun-chu-she-bei.md). # 25.1 USB Storage Devices Many external storage solutions, such as hard drives, USB flash drives, and CD and DVD burners, use the Universal Serial Bus (USB). FreeBSD supports USB 1.x, 2.0, and 3.0 devices. FreeBSD uses the umass(4) driver to access USB storage devices through the SCSI subsystem. The system treats USB devices as SCSI devices. This section describes how to verify that a USB storage device is recognized by FreeBSD and how to configure the device for use. ## Device Configuration To test the USB configuration, plug in the USB device. Use the `dmesg` command to confirm that the drive appears in the system message buffer, with output similar to the following: ```sh ugen2.2: at usbus2 umass0 on uhub3 umass0: on usbus2 umass0: SCSI over Bulk-Only; quirks = 0xc000 umass0:3:0: Attached to scbus3 (probe0:umass-sim0:0:0:0): REPORT LUNS. CDB: a0 00 00 00 00 00 00 00 00 10 00 00 (probe0:umass-sim0:0:0:0): CAM status: SCSI Status Error (probe0:umass-sim0:0:0:0): SCSI status: Check Condition (probe0:umass-sim0:0:0:0): SCSI sense: ILLEGAL REQUEST asc:20,0 (Invalid command operation code) (probe0:umass-sim0:0:0:0): Error 22, Unretryable error da0 at umass-sim0 bus 0 scbus3 target 0 lun 0 da0: Removable Direct Access SPC-4 SCSI device da0: Serial Number E0D55EA5359C1750989B07F6 da0: 400.000MB/s transfers da0: 59120MB (121077761 512 byte sectors) da0: quirks=0x2 ``` The brand (**Kingston DataTraveler 3.0**), device node (**da0**), speed (**400.000MB/s**), and capacity (**59120MB**) vary depending on the device. Since the system treats USB devices as SCSI devices, the `camcontrol` command can be used to list USB storage devices connected to the system: ```sh # camcontrol devlist at scbus3 target 0 lun 0 (da0,pass3) ......other irrelevant output omitted...... ``` The `usbconfig` command can also be used to list devices. ```sh # usbconfig ugen2.2: at usbus2, cfg=0 md=HOST spd=SUPER (5.0Gbps) pwr=ON (36mA) ......other irrelevant output omitted...... ``` ## Mounting a USB Drive The output above indicates that the USB device has been recognized as **/dev/da0**. If the device contains a partition table, its first partition is typically **/dev/da0p1**. If the device is formatted with a FAT32 file system, users can mount it to **/mnt** using the following command: ```sh # mount -t msdosfs /dev/da0p1 /mnt ``` Before unplugging the device, it must be unmounted first: ```sh # umount /mnt ``` After physically unplugging the device, the system message buffer will display a message similar to the following: ```sh ugen2.2: at usbus2 (disconnected) umass0: at uhub3, port 1, addr 1 (disconnected) da0 at umass-sim0 bus 0 scbus3 target 0 lun 0 da0: s/n E0D55EA5359C1750989B07F6 detached (da0:umass-sim0:0:0:0): Periph destroyed umass0: detached ``` ## Mounting USB Devices as a Regular User To allow regular users to mount devices, add all users who will use the device to the `operator` group. Next, ensure that the `operator` group can read and write to the device by adding the following lines to **/etc/devfs.rules**: ```ini [localrules=5] add path 'da*' mode 0660 group operator ``` > **Note** > > If other internal SCSI disks are also installed in the system, modify it as follows: > > ```ini > [localrules=5] > add path 'da[2-9]*' mode 0660 group operator > ``` > > This will exclude the first 2 SCSI disks (**da0** through **da1**) from the `operator` group. Replace **2** with the actual number of internal SCSI disks. Next, enable the ruleset in **/etc/rc.conf**: ```ini devfs_system_ruleset="localrules" ``` After that, require the system to allow regular users to mount file systems by adding the following line to **/etc/sysctl.conf**: ```ini vfs.usermount=1 ``` > **Warning** > > Although enabling `vfs.usermount` allows untrusted users to mount arbitrary media, this is not advisable from a security perspective. Most file systems are not designed to defend against malicious devices. This setting only takes effect after the next reboot. Finally, create a directory under which to mount the file system. The owner of this directory should be the user who will mount the file system. Use `root` to create a subdirectory owned by that user, such as **/mnt/username**. In the following example, replace **username** with the actual user name and **usergroup** with the user's primary group: ```sh # mkdir /mnt/username # chown username:usergroup /mnt/username ``` After that, a regular user can mount the USB storage device **/dev/da0p1**: ```sh $ mount -t msdosfs -o -m=644,-M=755 /dev/da0p1 /mnt/username ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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