CC @veblush these are some experiments I ran to debug the problems with ubuntu1604 workers. I still haven't figured out the best way to change docker's "data-root" on the new workers (in a way that's simple and works).

From the docker manual, --graph seems to be supported although it's marked deprecated. (link)

-g and --graph flags on dockerd
Deprecated In Release: v17.05.0

The -g or --graph flag for the dockerd or docker daemon command was used to indicate the directory in which to store persistent data and resource configuration and has been replaced with the more descriptive --data-root flag.

These flags were added before Docker 1.0, so will not be removed, only hidden, to discourage their use.

From the log, df doesn't have /tmpfs

Filesystem      Size  Used Avail Use% Mounted on
udev             60G     0   60G   0% /dev
tmpfs            12G  1.2M   12G   1% /run
/dev/sda1       291G  7.6G  283G   3% /
tmpfs            60G     0   60G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            60G     0   60G   0% /sys/fs/cgroup
/dev/loop0       90M   90M     0 100% /snap/core/6673
/dev/loop1       91M   91M     0 100% /snap/core/6350
/dev/loop4       58M   58M     0 100% /snap/google-cloud-sdk/77
/dev/loop5       55M   55M     0 100% /snap/google-cloud-sdk/68
/dev/sda15      105M  3.6M  101M   4% /boot/efi
/dev/loop6       97M   97M     0 100% /snap/core/9665
/dev/loop2       55M   55M     0 100% /snap/core18/1880
/dev/loop7      119M  119M     0 100% /snap/google-cloud-sdk/143
tmpfs            12G     0   12G   0% /run/user/1002

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