The /opt directory is most likely owned by root which is the super user on the system. On my ubuntu linux system, which will be very similar to yours, it's like so when I do a long listing for /opt as a non-root user:
~ $ ls -l /|grep opt
drwxr-xr-x 8 root root 4096 Jan 6 2012 opt
linux permissions have in general three categories of permissions: for the owner, a group of others who also have special permissions for that directory/file , and lastly everyone else.
first section of that listing above 'drwxr-xr-x' shows the permissions then the 'root root' shows owner (root) and group (root), then a size and date, followed by the name (opt)
from that the drwxr-xr-x shows first the type of resource, in this case 'd' for directory then read|write|execute (rwx) permissions for each of owner, group, and others in that order.
So in this case the owner (root) has read, write and execute permissions on /opt but the members of the group (root) have only read and execute permissions as do others.
It's that no write permissions for the group and others (the r-xr-x part) that prevent you running as 'myUser' from making a new directory in /opt
/opt is usually a place where third party software is installed, so it's not clear why you would want new users to be able to write to /opt since they could then for instance modify other software in /opt.
All users can by default, given the r-x permissions for everyone on /opt as shown, access /opt and read from it but not write to it.
However if you really want 'new users' to be able to write in /opt you have at least a couple of options:
- you can change the everyone permissions on /opt to rwx (not advisable); or
- you can change the group ownership of /opt to somethings else say 'optgroup' and make the group permissions rwx (leaving everyone else at r-x) and then add your new users to the group 'optgroup' that you created;
Be very cautious about giving permissions to new users for places they should not be able to alter.
Read more about linux file permissions at http://www.tuxfiles.org/linuxhelp/filepermissions.html