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[SOLVED] Tcpdump -w permission denied
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ats2
Apprentice
Apprentice


Joined: 22 Apr 2005
Posts: 297

PostPosted: Mon Jun 17, 2013 4:08 pm    Post subject: [SOLVED] Tcpdump -w permission denied Reply with quote

Hi all,

I have a strange behaviour with tcpdump on a gentoo box.

Code:
tcpdump -i eth0 -s0 -w /TMP/mydump.pcap


gives me permission denied. When I run it with strace, I get at the end:


Code:
fcntl64(3, F_GETFL)                     = 0x2 (flags O_RDWR)
fcntl64(3, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
recv(3, 0x3fa4806f, 1, MSG_TRUNC)       = -1 EAGAIN (Resource temporarily unavailable)
fcntl64(3, F_SETFL, O_RDWR)             = 0
setsockopt(3, SOL_SOCKET, SO_ATTACH_FILTER, "\1\0\0\0HE\34\10", 8) = 0
open("/TMP/mydump.pcap", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = -1 EACCES (Permission denied)
write(2, "tcpdump: ", 9tcpdump: )                = 9
write(2, "/TMP/mydump.pcap: Pe"..., 47/TMP/mydump.pcap: Permission denied) = 47
write(2, "\n", 1
)                       = 1
exit_group(1)                           = ?
+++ exited with 1 +++



The /TMP directory is owned by tcpdump and is writable...

Would you have any idea on how to solve this ?

Thanks. :)


Last edited by ats2 on Mon Jun 17, 2013 8:23 pm; edited 1 time in total
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bug_report
n00b
n00b


Joined: 17 Sep 2010
Posts: 68
Location: Frankfurt, Germany

PostPosted: Mon Jun 17, 2013 5:07 pm    Post subject: Reply with quote

Which USE flags does your tcpdump package have? chroot? suid?

Do you start tcpdump from 'root' or from a non-privileged user?
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NeddySeagoon
Administrator
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Joined: 05 Jul 2003
Posts: 31993
Location: 56N 3W

PostPosted: Mon Jun 17, 2013 6:55 pm    Post subject: Reply with quote

ats2,

tcpdump usually puts the interface into promiscious mode. That requires root privs.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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ats2
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Joined: 22 Apr 2005
Posts: 297

PostPosted: Mon Jun 17, 2013 8:23 pm    Post subject: Reply with quote

Thanks guys, found it: it was compiled with chroot use flag. recompiling it without solved the problem.
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