Ubuntu下U盘变成只读的解决方法

首先执行命令：

tail -f /var/log/syslog

然后插入有问题的U盘，tail会打印一些log：

Jan  :: zkw- kernel: [1451066.881318] usb -: new high-speed USB device number  using xhci_hcd
Jan  :: zkw- kernel: [1451066.898140] usb -: New USB device found, idVendor=, idProduct=
Jan  :: zkw- kernel: [1451066.898150] usb -: New USB device strings: Mfr=, Product=, SerialNumber=
Jan  :: zkw- kernel: [1451066.898156] usb -: Product: Cruzer Blade
Jan  :: zkw- kernel: [1451066.898161] usb -: Manufacturer: SanDisk
Jan  :: zkw- kernel: [1451066.898165] usb -: SerialNumber: 20060774101E0202EEDF
Jan  :: zkw- kernel: [1451066.898676] usb-storage -:1.0: USB Mass Storage device detected
Jan  :: zkw- kernel: [1451066.900344] scsi32 : usb-storage -:1.0
Jan  :: zkw- mtp-probe: checking bus , device : "/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1"
Jan  :: zkw- mtp-probe: bus: , device:  was not an MTP device
Jan  :: zkw- kernel: [1451067.898169] scsi :::: Direct-Access     SanDisk  Cruzer Blade     1.26 PQ:  ANSI:
Jan  :: zkw- kernel: [1451067.898785] sd :::: Attached scsi generic sg1 type
Jan  :: zkw- kernel: [1451067.899778] sd :::: [sdb]  -byte logical blocks: (8.00 GB/7.45 GiB)
Jan  :: zkw- kernel: [1451067.902348] sd :::: [sdb] Write Protect is off
Jan  :: zkw- kernel: [1451067.902352] sd :::: [sdb] Mode Sense:
Jan  :: zkw- kernel: [1451067.902656] sd :::: [sdb] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
Jan  :: zkw- kernel: [1451067.910687]  sdb: sdb4
Jan  :: zkw- kernel: [1451067.912366] sd :::: [sdb] Attached SCSI removable disk
Jan  :: zkw- kernel: [1451068.146809] FAT-fs (sdb4): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
Jan  :: zkw- udisksd[]: Mounted /dev/sdb4 at /media/zkw/ZHOU_KE_WEN on behalf of uid
Jan 23 09:40:56 zkw-3330 kernel: [1451068.395756] FAT-fs (sdb4): error, fat_get_cluster: invalid cluster chain (i_pos 0)
Jan 23 09:40:56 zkw-3330 kernel: [1451068.395761] FAT-fs (sdb4): Filesystem has been set read-only
Jan  :: zkw- wpa_supplicant[]: nl80211: send_and_recv->nl_recvmsgs failed: -

其中红色的部分表明了u盘出了问题，被挂在为只读的了，使用dosfsck修复一下：

umount /media/（U盘被挂在后的名字）
sudo dosfsck -v -a /dev/sdb4

修复后，u盘就回复读写了。