[Nexus 7 Android Development] CROSP:
Thank you for your prompt replies. The problem is that I cannot write anything to the sd partition. But I have noticed one interesting thing, when I try to create folder it tells me that I have no permission to create folder, but when I reconnect the device folder exists. Device is connected via MTP.

Any application is not able to find folder where to save a file.

There different errors appear in terminal logcat

01-21 12:44:27.742 150-436/? E/NetlinkEvent: NetlinkEvent::FindParam(): Parameter 'UID' not found
01-21 12:43:31.301 135-135/? E/GLConsumer: [com.android.systemui.ImageWallpaper] bindTextureImage: error binding external image: 0x502 START u0 {cmp=com.squareup.timessquare.sample/com.touchip.organizer.activities.AMenu_} from uid 10051 on display 0
01-21 12:43:25.214 567-592/? E/sdcard: opendir /data/media/0 failed: Permission denied
01-21 12:43:25.208 592-592/? W/sdcard: type=1400 audit(0.0:20): avc: denied { read } for name="0" dev=mmcblk0p9 ino=448803 scontext=u:r:sdcardd:s0 tcontext=u:object_r:system_data_file:s0 tclass=dir permissive=0
01-21 12:43:25.570 567-592/? E/sdcard: opendir /data/media/0 failed: Permission denied

So it seems that this storage is not mounted at all.

Output from mount command on the running device

rootfs on / type rootfs (ro,seclabel,relatime)
tmpfs on /dev type tmpfs (rw,seclabel,nosuid,relatime,mode=755)
devpts on /dev/pts type devpts (rw,seclabel,relatime,mode=600)
proc on /proc type proc (rw,relatime)
sysfs on /sys type sysfs (rw,seclabel,relatime)
selinuxfs on /sys/fs/selinux type selinuxfs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
none on /acct type cgroup (rw,relatime,cpuacct)
tmpfs on /mnt type tmpfs (rw,seclabel,relatime,mode=755,gid=1000)
none on /dev/memcg type cgroup (rw,relatime,memory)
none on /dev/cpuctl type cgroup (rw,relatime,cpu)
/dev/block/platform/sdhci-tegra.3/by-name/APP on /system type ext4 (ro,seclabel,relatime,user_xattr,acl,barrier=1)
/dev/block/platform/sdhci-tegra.3/by-name/CAC on /cache type ext4 (rw,seclabel,nosuid,nodev,noatime,errors=panic,user_xattr,acl,barrier=1,nomblk_io_submit,data=ordered)
/dev/block/platform/sdhci-tegra.3/by-name/UDA on /data type ext4 (rw,seclabel,nosuid,nodev,noatime,errors=panic,user_xattr,acl,barrier=1,nomblk_io_submit,data=ordered)
tmpfs on /storage type tmpfs (rw,seclabel,relatime,mode=755,gid=1000)
/dev/fuse on /mnt/runtime/default/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other)
/dev/fuse on /storage/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other)
/dev/fuse on /mnt/runtime/read/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other)
/dev/fuse on /mnt/runtime/write/emulated type fuse (rw,nosuid,nodev,noexec,noatime,user_id=1023,group_id=1023,default_permissions,allow_other

Using TWRP recovery

I installed ROM in the following way

1. Wipe All partitions (system,data.....)

2. Flash aosp_grouper-7.1.1-ota-eng-20170105.ds.zip

3. Reboot the device

I am not aware of latest androids internals, maybe something is wrong with vold.fstab file

---------- Post added at 03:01 PM ---------- Previous post was at 02:50 PM ----------

I have just found interesting message when device is booting, btw these are first messages when logcat is available.

01-21 12:58:13.250 115 115 W auditd : type=2000 audit(0.0:1): initialized
01-21 12:58:13.980 115 115 I auditd : type=1403 audit(0.0:2): policy loaded auid=4294967295 ses=4294967295
01-21 12:58:13.980 115 115 W auditd : type=1404 audit(0.0:3): enforcing=1 old_enforcing=0 auid=4294967295 ses=4294967295
01-21 12:58:14.980 1 1 W init : type=1400 audit(0.0:4): avc: denied { create } for name="sdcard" scontext=u:r:init:s0 tcontext=u:object_r:tmpfs:s0 tclass=lnk_file permissive=0