www-data user can't write to /tmp folder

Question

Linux 4.4.0-75-generic #96-Ubuntu SMP Thu Apr 20 09:56:33 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Permissions seem wide open

>>> ll /
...
drwxrwxrwt   8 root   root         4096 May  1 02:44 tmp/

Denied access:

sudo -u www-data echo "hello" > /tmp/test.txt
-bash: /tmp/test.txt: Permission denied

Disk space seems OK:

>>> df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            980M     0  980M   0% /dev
tmpfs           200M  8.2M  192M   5% /run
/dev/xvda1      7.8G  6.3G  1.1G  86% /
tmpfs          1000M     0 1000M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs          1000M     0 1000M   0% /sys/fs/cgroup
cgmfs           100K     0  100K   0% /run/cgmanager/fs
tmpfs           200M     0  200M   0% /run/user/1000

Solution

Probably the file already exists. In this case, if it has been created by another process already, the system will not allow you to either modify or delete it since you're not the owner. In this case, right after the file is created, you might want to

chmod 666 /tmp/test.txt

I had the same exact problem, and this was the solution.

Comments

[Admin]

Check your selinux logs.

[Admin]

@EEAA Is selinux used in Ubuntu 16?

[Admin]

Just use /dev/shm instead of tmp. Your apps will run even faster that way...

[Admin]

Is there a /tmp/test.txt file already? What is the output of ls -alh /tmp/test.txt.

[Stephane]

In my case, the file does not yet exist serverfault.com/q/1074904/249412