I made this stupid mistake and it take me some time.

Sticky bit for script file not work

for script file

user:coolder

  1. cat check_euid.sh 
  2. echo $EUID
  1. ➜  Bin bash check_euid.sh 
  2. 1000

change owner to root:root

  1. ➜  Bin sudo chown root:root check_euid.sh

add sticky bit for the script

  1. ➜  Bin sudo chmod +s check_euid.sh

$EUID will not change !!!

  2. ➜  Bin ls
  3. a.c  a.out  check_euid.sh
  4. ➜  Bin sudo chown root:root check_euid.sh 
  5. ➜  Bin sudo chmod +s check_euid.sh 
  6. ➜  Bin whoami
  7. coolder
  8. ➜  Bin bash check_euid.sh 
  9. 1000
  10. ➜  Bin

for binary file

user:coolder

  1. ➜  Bin cat a.c
  2. #include<unistd.h>
  3. #include<sys/types.h>
  5. int main(void)
  6. {
  7.     printf("%d %d", getuid(), geteuid());
  8. }

compile and run

  1. ➜  Bin ./a.out 
  2. 1000 1000%

effect on binary file !!!

  1. ➜  Bin sudo chown root:root a.out 
  2. ➜  Bin sudo chmod +s a.out
  3. ➜  Bin ./a.out 
  4. 1000 0%