a) Can anybody write in the tmp subfolder of the root?
对，根下的tmp子目录为临时目录，默认权限为drwxrwxrwt，允许任何人写入。b) Can anybody read and run from the bin subfolder of the root?
对，默认权限设置都是允许运行/bin下的程序。
c) Can the admin write in the sys subfolder of the root?
否，/sys是特殊的内核文件系统
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)d) Can anybody make a change from the var subfolder of the root?
否，默认权限不允许root用户以外的用户更改/varls -ld /var
drwxr-xr-x 14 root root 4096 Jan 292015 /var
a) You can do anything you want, nobody else can do a thing
mkdir test_a
chmod 700 test_ab) You can do anything, and others might see it, but they can't run it or change it
mkdir test_b
chmod 755 test_bc) Everybody including yourself can see it, only you and members of your groups can run or change it
mkdir test_c
chmod 775d) You and members of your group can run it and see it, those outside the group can't do anything
mkdir test_d
chmod 770