I noticed a strange difference in /proc/pid/fd/ directory when a command is executed via /usr/bin/sudo. Say, there are three files in some directory. (In my environment, /tmp/ is a plain ext4 partition.) # touch /tmp/1 # touch /tmp/2 # touch /tmp/3 # ls -l /tmp/? -rw-r--r-- 1 root root 0 May 2 21:48 /tmp/1 -rw-r--r-- 1 root root 0 May 2 21:48 /tmp/2 -rw-r--r-- 1 root root 0 May 2 21:48 /tmp/3 Try to read one of them using "tail -f" from one terminal. # tail -f /tmp/1 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:54 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:54 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:54 2 -> /dev/pts/0 lr-x------ 1 root root 64 May 2 21:54 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:54 4 -> anon_inode:inotify Quit the "tail -f". Try to read two of them using "tail -f". # tail -f /tmp/1 /tmp/2 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:54 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:54 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:54 2 -> /dev/pts/0 lr-x------ 1 root root 64 May 2 21:54 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:54 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:54 5 -> anon_inode:inotify Quit the "tail -f". Try to read three of them using "tail -f". # tail -f /tmp/1 /tmp/2 /tmp/3 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:55 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:55 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:55 2 -> /dev/pts/0 lr-x------ 1 root root 64 May 2 21:55 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:55 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:55 5 -> /tmp/3 lr-x------ 1 root root 64 May 2 21:55 6 -> anon_inode:inotify Quit the "tail -f". You see, they are all fine. However, the output is different when executed via /usr/bin/sudo . Try to read one of them using "sudo tail -f" from one terminal. # sudo tail -f /tmp/1 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:55 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:55 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:55 2 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:55 3 -> /tmp/1 lrwx------ 1 root root 64 May 2 21:55 4 -> anon_inode:inotify Quit the "tail -f". Try to read two of them using "sudo tail -f". # sudo tail -f /tmp/1 /tmp/2 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:56 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 2 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 3 -> /tmp/1 lrwx------ 1 root root 64 May 2 21:56 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:56 5 -> anon_inode:inotify Quit the "tail -f". Try to read three of them using "sudo tail -f". # sudo tail -f /tmp/1 /tmp/2 /tmp/3 Show /proc/pid/fd/ from another terminal. # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:56 0 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 1 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 2 -> /dev/pts/0 lrwx------ 1 root root 64 May 2 21:56 3 -> /tmp/1 lrwx------ 1 root root 64 May 2 21:56 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:56 5 -> /tmp/3 lr-x------ 1 root root 64 May 2 21:56 6 -> anon_inode:inotify Quit the "tail -f". You see, when executed via /usr/bin/sudo , fd == 3 and fd == 4 are reported as "lrwx------" whereas fd >= 5 are reported as "lr-x------". # strace -f -e open sudo tail -f /tmp/1 /tmp/2 /tmp/3 shows that /usr/bin/tail is opening /tmp/1 /tmp/2 /tmp/3 as O_RDONLY. /usr/bin/sudo can't set w bit before /usr/bin/tail opens them with r bit. I wonder from where the w bit came... Above result was obtained using kernel 3.2.0-24-generic-pae (3.2.0-24.37) on Ubuntu 12.04, but below result (similar but not identical) was obtained using vanilla 3.4-rc5 kernel on CentOS 6.2. -- (normal case. normal result.) # tail -f /tmp/1 /tmp/2 # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:04 0 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:04 1 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:04 2 -> /dev/pts/2 lr-x------ 1 root root 64 May 2 21:04 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:04 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:04 5 -> anon_inode:inotify -- (sudo case. only fd == 3 got w bit.) # sudo tail -f /tmp/1 /tmp/2 # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:05 0 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:05 1 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:05 2 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:05 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:05 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:05 5 -> anon_inode:inotify -- (normal case. normal result.) # tail -f /tmp/1 /tmp/2 /tmp/3 # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:07 0 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:07 1 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:07 2 -> /dev/pts/2 lr-x------ 1 root root 64 May 2 21:07 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:07 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:07 5 -> /tmp/3 lr-x------ 1 root root 64 May 2 21:07 6 -> anon_inode:inotify -- (sudo case. fd == 3 and fd == 6 got w bit.) # sudo tail -f /tmp/1 /tmp/2 /tmp/3 # ls -l /proc/`pidof tail`/fd/ total 0 lrwx------ 1 root root 64 May 2 21:07 0 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:07 1 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:07 2 -> /dev/pts/2 lrwx------ 1 root root 64 May 2 21:07 3 -> /tmp/1 lr-x------ 1 root root 64 May 2 21:07 4 -> /tmp/2 lr-x------ 1 root root 64 May 2 21:07 5 -> /tmp/3 lrwx------ 1 root root 64 May 2 21:07 6 -> anon_inode:inotify I guess something is wrong. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
