Geek Answers Handbook

Why can I write "mnt / sdcard" and not "mnt / extsd"?

I am trying to save a file to external storage (Android 4.2.2).

I am using the correct permission in the manifest.xml file:

<manifest ...> ... <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/> ...

An external SD card is available, I can prove it with another application for reading and writing files. The path / mnt / extsd / is valid, look at the image below. An external SD card is writable because I can copy / paste files into it.

enter image description here

Code:

 try { String path = "/mnt/extsd/file.dat" File f = new File(path); f.createNewFile(); return true; } catch (Exception e) { e.printStackTrace(); return false; }

I get an error on f.createNewFile(); :

 W/System.err(2172): java.io.IOException: open failed: EACCES (Permission denied) W/System.err(2172): at java.io.File.createNewFile(File.java:948) W/System.err(2172): at solarapp.activities.settings.application.ActivityBackup$BackupTask.doInBackground(ActivityBackup.java:77) W/System.err(2172): at solarapp.activities.settings.application.ActivityBackup$BackupTask.doInBackground(ActivityBackup.java:1) W/System.err(2172): at android.os.AsyncTask$2.call(AsyncTask.java:287) W/System.err(2172): at java.util.concurrent.FutureTask.run(FutureTask.java:234) W/System.err(2172): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) W/System.err(2172): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) W/System.err(2172): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) W/System.err(2172): at java.lang.Thread.run(Thread.java:856) W/System.err(2172): Caused by: libcore.io.ErrnoException: open failed: EACCES (Permission denied) W/System.err(2172): at libcore.io.Posix.open(Native Method) W/System.err(2172): at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110) W/System.err(2172): at java.io.File.createNewFile(File.java:941)

If I use String path = "/mnt/extsd/file.dat" , everything works fine! So where is the problem?

EDIT

I use this solution to get a list of available repositories:

How to get a list of connected external storage of an Android device

And, as suggested, I send the result of the adb shell cat /proc/mounts :

 rootfs / rootfs rw 0 0 tmpfs /dev tmpfs rw,nosuid,relatime,mode=755 0 0 devpts /dev/pts devpts rw,relatime,mode=600 0 0 proc /proc proc rw,relatime 0 0 sysfs /sys sysfs rw,relatime 0 0 none /acct cgroup rw,relatime,cpuacct 0 0 tmpfs /mnt/secure tmpfs rw,relatime,mode=700 0 0 tmpfs /mnt/asec tmpfs rw,relatime,mode=755,gid=1000 0 0 tmpfs /mnt/obb tmpfs rw,relatime,mode=755,gid=1000 0 0 none /dev/cpuctl cgroup rw,relatime,cpu 0 0 debugfs /sys/kernel/debug debugfs rw,relatime 0 0 /dev/block/by-name/system /system ext4 ro,relatime,data=ordered 0 0 /dev/block/by-name/cache /cache ext4 rw,nosuid,nodev,noatime,nomblk_io_submit,data=ordered 0 0 /dev/block/by-name/data /data ext4 rw,nosuid,nodev,noatime,nomblk_io_submit,noauto_da_alloc,data=ordered 0 0 /dev/block/vold/93:72 /mnt/sdcard vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0 /dev/block/vold/93:72 /mnt/secure/asec vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1015,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0 tmpfs /mnt/sdcard/.android_secure tmpfs ro,relatime,size=0k,mode=000 0 0 /dev/block/vold/179:1 /mnt/extsd vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1000,gid=1023,fmask=0702,dmask=0702,allow_utime=0020,codepage=cp437,iocharset=ascii,shortname=mixed,utf8,errors=remount-ro 0 0

Response to adb shell cat /proc/partitions

  major minor #blocks name 93 0 32768 nanda 93 8 16384 nandb 93 16 16384 nandc 93 24 786432 nandd 93 32 1048576 nande 93 40 16384 nandf 93 48 32768 nandg 93 56 524288 nandh 93 64 131072 nandi 93 72 4409344 nandj 179 0 3849216 mmcblk0 179 1 3845120 mmcblk0p1

Response to the adb shell cat /proc/devices and adb shell ls -l /mnt

 Character devices: 1 mem 4 /dev/vc/0 4 tty 5 /dev/tty 5 /dev/console 5 /dev/ptmx 7 vcs 10 misc 13 input 29 fb 81 video4linux 100 telephony 108 ppp 116 alsa 128 ptm 136 pts 150 cedar_dev 166 ttyACM 180 usb 188 ttyUSB 189 usb_device 216 rfcomm 247 lcd 248 capture 249 disp 250 ttyGS 251 ttyS 252 sunxi_pwm 253 bsg 254 rtc Block devices: 259 blkext 7 loop 8 sd 65 sd 66 sd 67 sd 68 sd 69 sd 70 sd 71 sd 93 nand 128 sd 129 sd 130 sd 131 sd 132 sd 133 sd 134 sd 135 sd 179 mmc 254 device-mapper /system/bin/sh: cat: and: No such file or directory /system/bin/sh: cat: adb: No such file or directory /system/bin/sh: cat: shell: No such file or directory /system/bin/sh: cat: ls: No such file or directory /system/bin/sh: cat: -l: No such file or directory /system/bin/sh: cat: /mnt: Is a directory

Reply to adb shell ls -l /mnt

 drwxr-xr-x root system 2014-04-22 11:56 asec d---rwxr-x system media_rw 1970-01-01 01:00 extsd drwxrwx--- media_rw media_rw 2014-04-22 11:56 media drwxr-xr-x root system 2014-04-22 11:56 obb d---rwxr-x system sdcard_rw 2014-04-22 12:26 sdcard drwx------ root root 2014-04-22 11:56 secure drwx------ shell shell 2014-04-22 11:56 shell d--------- system system 2014-04-22 11:56 usbhost1
+6
source share
1 answer
 Response to the command adb shell ls -l /mnt d---rwxr-x system media_rw 1970-01-01 01:00 extsd

To write extsd process must be part of the media_rw group, but WRITE_EXTERNAL_STORAGE add it to the sdcard_rw group. The required permission is WRITE_MEDIA_STORAGE , but, unfortunately, its signatureOrSystem level of protection, so you cannot use it in your application

+1
source

More articles:


All Articles