[Note: This similar Q concerns the same bash error message. It's been marked a duplicate of this other Q. But because I found a very different source for this error, I will answer my own Q below.]
This previously working bash script line
while ... do ... done <<< "$foo" one day started producing this error message:
cannot create temp file for here-document: Permission denied
In my case I altered the /tmp directory default permissions (I think I've changed by mistake to 0777).
The solution was to revert it back to the default /tmp permission, which is 1777 in octal (1=sticky bit, 7=R+W+X).
So in a nutshell sudo chmod -R 1777 /tmp should fix the problem.
-R flag. No reason to change everyone's files below /tmp to be read-write-executable by everyone. Some of those files are sensitive to the security of your users. I had added umask 777 before the here string. After removing the umask, the error went away. So lesson learned: There is a temporary file created for a here string (<<<), and this is related to a here document (<<), and you must have an appropriate umask set for these to work.
my personal experience with this problem was with umask binary notation, just like @eliptical-view. I supposed that writing:
umask 0644 would give me read and write access to the files I created, what's wrong
After I changed the umask to be
umask 0022 the error disappeared.
Actually, the binary notation should be understood as a binary complement.
So, in the umask's mask below when one writes 0 for the file owner, this user will have total access to the files he or she creates. The value 2 means the 2nd bit is masked, what means in this case, by default the other users will not be allowed to write to the files the file owner creates.
umask, for precisely three bits are involved in Posix file permissions -- for the owner, one of his or her groups, and everybody else.
ima_policy=appraise_tcbkernel parameter) with combination of/tmpnot beingtmpfs. But this is not really a common case :).