Cannot delete php/sessions folder

Question

I could really use some help. I have a Ubuntu 14.04.6 account with DigitalOcean and am encountering some errors related to lack of space. When I ssh into the account and do a tab-completion at the command line, I get the error:

bash: cannot create temp file for here-document: No space left on device

If I run df -h I get

Filesystem      Size  Used Avail Use% Mounted on
udev            233M  4.0K  233M   1% /dev
tmpfs            49M  876K   49M   2% /run
/dev/vda1        20G  8.2G   11G  44% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
none            5.0M     0  5.0M   0% /run/lock
none            245M     0  245M   0% /run/shm
none            100M     0  100M   0% /run/user

However, if I do df -i I get

Filesystem      Inodes   IUsed IFree IUse% Mounted on
udev             59582     404 59178    1% /dev
tmpfs            62700     334 62366    1% /run
/dev/vda1      1310720 1310720     0  100% /
none             62700       3 62697    1% /sys/fs/cgroup
none             62700       4 62696    1% /run/lock
none             62700       1 62699    1% /run/shm
none             62700       2 62698    1% /run/user

and I get all sorts of space errors when I try to do various tasks.

I figured the issue was something related to /dev/vda1. Upon searching the issue online, it seemed that this was related to PHP sessions files not deleting. Indeed, I tried:

ls -l /var/lib/php
total 66772
drwxr-xr-x 3 root root     4096 Mar 16  2019 modules
drwx-wx-wt 2 root root 68366336 Dec 29 04:27 sessions

I understand I need to dig into the automated cron tasks and figure out why things are not being deleted. However, firstly I need enough space to actually do some work. But I'm at my wits end of how to delete the contents of this folder. I've tried:

sudo find /var/lib/php/sessions -name "sess_*" -exec rm {} \;

sudo find /var/lib/php/sessions -type f -delete

sudo sh -c "rm -rf /var/lib/php/sessions/*"

None of them seem to do anything upon issuing the command.

Update 14 Mar 2020: I encountered this error again, and again I had difficulty deleting the files. However, at the very least I found a solution to the deletion problem [3]. The solution is to use rsync to delete. I did the following

cd /var/lib/php
sudo mkdir emptydir
rsync -a --delete /var/lib/php/emptydir/ /var/lib/php/sessions/

Source:

[1] PHP session directory full?

[2] PHP sessions directory keeps filling until overflowing

[3] https://unix.stackexchange.com/questions/37329/efficiently-delete-large-directory-containing-thousands-of-files