>>> Ryan Mallon <rmal...@gmail.com> schrieb am 09.07.2012 um 01:24 in Nachricht <4ffa16b6.9050...@gmail.com>: > On 06/07/12 16:27, Ulrich Windl wrote: > > Hi! > > > > Recently I found a problem with the command (kernel 3.0.34-0.7-default from > SLES 11 SP2, run as root): > > test -r "$file" && cat "$file" > > emitting "Permission denied" > > > > Investigating, I found that "test" actually uses "access()" to check for > permissions. Unfortunately there are some files in /sys that have > "write-only" > permission bits set (e.g. /sys/devices/system/cpu/probe). > > > > ~ # ll /sys/devices/system/cpu/probe > > --w------- 1 root root 4096 Jun 29 12:43 /sys/devices/system/cpu/probe > > ~ # F=/sys/devices/system/cpu/probe > > ~ # test "$F" && cat "$F" > > cat: /sys/devices/system/cpu/probe: Permission denied > > Looks like you have a typo here, I think you wanted "test -r $F", not > "test $F", the latter will just evaluate "$F" as an expression which > will be true, and so you get the permission denied error running cat.
Hi! You are right: It's a typo, but only in the message; the actual test was done correctly, and the outcome is quite the same. > > Using "test -r $F" on a write-only sysfs file correctly returns false on > my machine (Ubuntu 10.04.4 LTS/2.6.32-41-generic). Not here, unfortunately: # ll /sys/devices/system/cpu/probe --w------- 1 root root 4096 Jul 2 11:52 /sys/devices/system/cpu/probe # F=/sys/devices/system/cpu/probe # test -r "$F" && cat "$F" cat: /sys/devices/system/cpu/probe: Permission denied # uname -a Linux h07 2.6.32.59-0.3-default #1 SMP 2012-04-27 11:14:44 +0200 x86_64 x86_64 x86_64 GNU/Linux Regards, Ulrich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
