/tmp has been reported to be read-only filesystem

Question

Environment: Up to dated rasbian.

pi@raspberrypi:/etc $ cat os-release 
PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=raspbian
ID_LIKE=debian
HOME_URL="http://www.raspbian.org/"
SUPPORT_URL="http://www.raspbian.org/RaspbianForums"
BUG_REPORT_URL="http://www.raspbian.org/RaspbianBugs"
pi@raspberrypi:/etc $ 

I would like to make my RPI to a Bluetooth speaker as I can connect it to my speaker system with HDMI. And I followed this answer. However, it turns out that there is no audio output after I successfully paired and connected it to my phone. But omxplayer works fine.

After a few investigations, I found that there is something wrong with pulseaudio. I found those issues from syslog

pulseaudio[895]: [autospawn] core-util.c: Failed to create random directory /tmp/pulse-jQKTIx5u3FhO: Read-only file system 
pulseaudio[895]: [autospawn] lock-autospawn.c: Cannot access autospawn lock. 
pulseaudio[895]: [pulseaudio] main.c: Failed to acquire autospawn lock 
systemd-udevd[855]: Process '/usr/lib/udev/bluetooth' failed with exit code 1. 
systemd-udevd[853]: Process '/usr/sbin/th-cmd --socket /var/run/thd.socket --passfd --udev' failed with exit code 1.

I am confused that /tmp is writeable from shell --- both mkdir and touch works fine.

And it seems that there is nothing wrong with /tmp

pi@raspberrypi:/etc $ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        30G  5.3G   23G  19% /
devtmpfs        460M     0  460M   0% /dev
tmpfs           464M     0  464M   0% /dev/shm
tmpfs           464M   13M  452M   3% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           464M     0  464M   0% /sys/fs/cgroup
/dev/mmcblk0p1   41M   22M   20M  53% /boot
tmpfs            93M  4.0K   93M   1% /run/user/1000
pi@raspberrypi:/etc $ ls -dhl /tmp
drwxrwxrwt 16 root root 4.0K Mar 18 14:32 /tmp
pi@raspberrypi:/etc $ cat fstab 
proc            /proc           proc    defaults          0       0
PARTUUID=98e0451d-01  /boot           vfat    defaults          0       2
PARTUUID=98e0451d-02  /               ext4    defaults,noatime  0       1
# a swapfile is not a swap partition, no line here
#   use  dphys-swapfile swap[on|off]  for that
pi@raspberrypi:/etc $ 

I really have no idea what's going on.

Update:

Here comes the output of mount command:

/dev/mmcblk0p2 on / type ext4 (rw,noatime,data=ordered)
devtmpfs on /dev type devtmpfs (rw,relatime,size=470128k,nr_inodes=117532,mode=755)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=25,pgrp=1,timeout=0,minproto=5,maxproto=5,direct)
sunrpc on /run/rpc_pipefs type rpc_pipefs (rw,relatime)
debugfs on /sys/kernel/debug type debugfs (rw,relatime)
mqueue on /dev/mqueue type mqueue (rw,relatime)
configfs on /sys/kernel/config type configfs (rw,relatime)
/dev/mmcblk0p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,errors=remount-ro)
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=94944k,mode=700,uid=1000,gid=1000)
gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)
fusectl on /sys/fs/fuse/connections type fusectl (rw,relatime)

Answer 1

I just opened this issue--seems similar to yours, at least the read-only filesystem part.

Link to issue

However, I'm not using pulse-audio and can stream from a connected bluetooth device using an A2DP profile. Apparently, it's not needed and can cause issues on stretch.