Home / ubuntu / Questions / 633857
Accepted
Luis Masuelli
Asked: 2015-06-09 09:45:15 +0800 CST

Why I can't write a file in /tmp/ even when it is root:root and has "t" flag?

  • 772

I am using the postgres user to execute some special commands. For that, I am trying the following:

$ sudo su - postgres  
postgres$ ls -l /tmp
drwxrwxrwt  13 root root  4096 jun  8 12:20 tmp  

PGPASSWORD=mypasswordhere time pg_dump --username=postgres --no-password -f /tmp/myfilehere.sql mydatabasehere
pg_dump: [archiver] could not open output file "/tmp/myfilehere.sql": Permiso denegado  
Command exited with non-zero status 1  
0.25user 0.06system 0:02.04elapsed 15%CPU (0avgtext+0avgdata 58064maxresident)k  
0inputs+0outputs (0major+5110minor)pagefaults 0swaps

Question: Why can't I write in /tmp with user postgres? Noticing the sticky flag is set on /tmp.

command-line

1 Answers

  1. Best Answer

    The sticky bit will prevent any user other than the owner of file (and owner of directory and root) to remove/rename any file inside the directory containing sticky bit. If any user does not have permission to write then he would not be able to create any file in /tmp or any other directory having sticky bit set, same goes for read and execute operations.

    In your case if postgres has sufficient permission to read/write/execute files in /tmp then he can do that otherwise you need to set the appropriate permissions manually.

    Example :

    drwxrwxrwt   7 root   root    4096 Jun  9 00:41 tmp

$ sudo chmod o-rwx /tmp

drwxrwx--T   7 root   root    4096 Jun  9 00:41 tmp

$ touch /tmp/foo.txt
touch: cannot touch ‘/tmp/foo.txt’: Permission denied

$ sudo chmod o+rwx /tmp

$ touch /tmp/foo.txt

$ ls -l /tmp/
-rw-rw-r-- 1 user user    0 Jun  9 00:50 foo.txt
    • 9