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Why does lsof complain about tracefs?

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margin-bottom:0;

9

2

Every execution of lsof issues a warning about the TraceFS:

$ lsof any-file
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
 Output information may be incomplete.

$ mount | grep trace
tracefs on /sys/kernel/debug/tracing type tracefs (rw,relatime)

(This is on Ubuntu 15.10, fully updated)

Is it normal for TraceFS to be mounted during normal operation?

If so, how can I tell lsof to skip it?

filesystem lsof

share|improve this question

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

add a comment
 | 

9

2

Every execution of lsof issues a warning about the TraceFS:

$ lsof any-file
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
 Output information may be incomplete.

$ mount | grep trace
tracefs on /sys/kernel/debug/tracing type tracefs (rw,relatime)

(This is on Ubuntu 15.10, fully updated)

Is it normal for TraceFS to be mounted during normal operation?

If so, how can I tell lsof to skip it?

filesystem lsof

share|improve this question

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

add a comment
 | 

Every execution of lsof issues a warning about the TraceFS:

$ lsof any-file
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
 Output information may be incomplete.

$ mount | grep trace
tracefs on /sys/kernel/debug/tracing type tracefs (rw,relatime)

(This is on Ubuntu 15.10, fully updated)

Is it normal for TraceFS to be mounted during normal operation?

If so, how can I tell lsof to skip it?

filesystem lsof

share|improve this question

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

$ lsof any-file
lsof: WARNING: can't stat() tracefs file system /sys/kernel/debug/tracing
 Output information may be incomplete.

$ mount | grep trace
tracefs on /sys/kernel/debug/tracing type tracefs (rw,relatime)

share|improve this question

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

share|improve this question

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

asked Mar 21 '16 at 11:17

ZilkZilk

20011 silver badge99 bronze badges

asked Mar 21 '16 at 11:17

ZilkZilk

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4 Answers
4

active

oldest

votes

10

The answer to your question is in the file permissions:

try:

$ ls -l /sys/kernel/debug/tracing
ls: cannot access '/sys/kernel/debug/tracing': Permission denied
$ ls -l /sys/kernel
total 0
...
drwx------ 31 root root 0 2016-06-15 11:06:47 debug
...

So, normal users are not allowed to access /sys/kernel/debug/tracing and there seems to be no way to ask lsof to avoid accessing it.

We could then discuss whether this is a bug or not, but the answer to your question boils down to this.

share|improve this answer

edited Jun 15 '16 at 10:17

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  What do you mean "bug"? "lsof" needs to be executed with "sudo" or as "root".
  
  – Rinzwind
  Jun 15 '16 at 10:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  lsof doesn't need to be run as root. We can discuss about its security (see man lsof) but it definitely doesn't need to be run only with superuser grants. It sits in /usr/bin not in /usr/sbin.
  
  – EnzoR
  Jun 15 '16 at 10:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "No way to avoid it" is a perfectly acceptable answer. Besides, it appears that TraceFS no longer gets mounted by default as of Ubuntu 16.04; the warning when running lsof as a normal user has now disappeared.
  
  – Zilk
  Jun 16 '16 at 20:20
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I'm on 16.04, it hasn't disappeared - still an issue.
  
  – TenLeftFingers
  Oct 27 '16 at 15:41
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @TenLeftFingers It's working in my up-to-date Kubuntu 16.04!
  
  – EnzoR
  Oct 27 '16 at 16:24
  

  
  
  
  

 | 
show 2 more comments

3

I had the same problem and this answer helped me to understand the problem a little better.

I've found out that one way to remove the annoying warning is to umount debugfs

mount | grep debugfs 
none on /sys/kernel/debug type debugfs (rw,_netdev)

sudo umount $(mount | grep debugfs | awk 'print $3')

If you now run lsof there is no warning.

share|improve this answer

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this is really why I came looking. I don't care so much why the error is showing up. I really just want it to go away. Thanks damko!
  
  – cjac
  Jan 22 '18 at 21:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  umount: /sys/kernel/debug: target is busy.
  
  – msangel
  Aug 4 at 0:34
  

  
  
  
  

add a comment
 | 

2

The issue is that you do not have permission to access the debugfs directory. The tracefs directory was created to allow people to mount the tracing directory directly at /sys/kernel/tracing and not require enabling debugfs. But for backward compatibility, when mounting the debugfs directory, it would automatically mount tracefs in the "tracing" directory of debugfs.

Now when you perform lsof it looks at the /proc/filesystems file as well as /proc/mounts. It sees that tracefs is mounted at /sys/kernel/debug/tracing, and thus tries to stat it. Unfortunately, because /sys/kernel/debug wont let non-root users see inside of it, you get the error message when trying to stat the directory "tracing" from within /sys/kernel/debug. If you unmount the debugfs directory, the warning will go away.

share|improve this answer

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

add a comment
 | 

0

The Warning is written to stderr. You can always just redirect this to the /dev/null:

lsof <any-file> 2>/dev/null

Cheers,

share|improve this answer

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

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 | 

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10

The answer to your question is in the file permissions:

try:

$ ls -l /sys/kernel/debug/tracing
ls: cannot access '/sys/kernel/debug/tracing': Permission denied
$ ls -l /sys/kernel
total 0
...
drwx------ 31 root root 0 2016-06-15 11:06:47 debug
...

So, normal users are not allowed to access /sys/kernel/debug/tracing and there seems to be no way to ask lsof to avoid accessing it.

We could then discuss whether this is a bug or not, but the answer to your question boils down to this.

share|improve this answer

edited Jun 15 '16 at 10:17

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  What do you mean "bug"? "lsof" needs to be executed with "sudo" or as "root".
  
  – Rinzwind
  Jun 15 '16 at 10:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  lsof doesn't need to be run as root. We can discuss about its security (see man lsof) but it definitely doesn't need to be run only with superuser grants. It sits in /usr/bin not in /usr/sbin.
  
  – EnzoR
  Jun 15 '16 at 10:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "No way to avoid it" is a perfectly acceptable answer. Besides, it appears that TraceFS no longer gets mounted by default as of Ubuntu 16.04; the warning when running lsof as a normal user has now disappeared.
  
  – Zilk
  Jun 16 '16 at 20:20
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I'm on 16.04, it hasn't disappeared - still an issue.
  
  – TenLeftFingers
  Oct 27 '16 at 15:41
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @TenLeftFingers It's working in my up-to-date Kubuntu 16.04!
  
  – EnzoR
  Oct 27 '16 at 16:24
  

  
  
  
  

 | 
show 2 more comments

10

The answer to your question is in the file permissions:

try:

$ ls -l /sys/kernel/debug/tracing
ls: cannot access '/sys/kernel/debug/tracing': Permission denied
$ ls -l /sys/kernel
total 0
...
drwx------ 31 root root 0 2016-06-15 11:06:47 debug
...

So, normal users are not allowed to access /sys/kernel/debug/tracing and there seems to be no way to ask lsof to avoid accessing it.

We could then discuss whether this is a bug or not, but the answer to your question boils down to this.

share|improve this answer

edited Jun 15 '16 at 10:17

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  What do you mean "bug"? "lsof" needs to be executed with "sudo" or as "root".
  
  – Rinzwind
  Jun 15 '16 at 10:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  lsof doesn't need to be run as root. We can discuss about its security (see man lsof) but it definitely doesn't need to be run only with superuser grants. It sits in /usr/bin not in /usr/sbin.
  
  – EnzoR
  Jun 15 '16 at 10:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "No way to avoid it" is a perfectly acceptable answer. Besides, it appears that TraceFS no longer gets mounted by default as of Ubuntu 16.04; the warning when running lsof as a normal user has now disappeared.
  
  – Zilk
  Jun 16 '16 at 20:20
  

  
  
  
  


• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  I'm on 16.04, it hasn't disappeared - still an issue.
  
  – TenLeftFingers
  Oct 27 '16 at 15:41
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @TenLeftFingers It's working in my up-to-date Kubuntu 16.04!
  
  – EnzoR
  Oct 27 '16 at 16:24
  

  
  
  
  

 | 
show 2 more comments

The answer to your question is in the file permissions:

try:

$ ls -l /sys/kernel/debug/tracing
ls: cannot access '/sys/kernel/debug/tracing': Permission denied
$ ls -l /sys/kernel
total 0
...
drwx------ 31 root root 0 2016-06-15 11:06:47 debug
...

So, normal users are not allowed to access /sys/kernel/debug/tracing and there seems to be no way to ask lsof to avoid accessing it.

We could then discuss whether this is a bug or not, but the answer to your question boils down to this.

share|improve this answer

edited Jun 15 '16 at 10:17

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

$ ls -l /sys/kernel/debug/tracing
ls: cannot access '/sys/kernel/debug/tracing': Permission denied
$ ls -l /sys/kernel
total 0
...
drwx------ 31 root root 0 2016-06-15 11:06:47 debug
...

share|improve this answer

edited Jun 15 '16 at 10:17

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

answered Jun 15 '16 at 9:43

EnzoREnzoR

1,2501212 silver badges2626 bronze badges

3

I had the same problem and this answer helped me to understand the problem a little better.

I've found out that one way to remove the annoying warning is to umount debugfs

mount | grep debugfs 
none on /sys/kernel/debug type debugfs (rw,_netdev)

sudo umount $(mount | grep debugfs | awk 'print $3')

If you now run lsof there is no warning.

share|improve this answer

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this is really why I came looking. I don't care so much why the error is showing up. I really just want it to go away. Thanks damko!
  
  – cjac
  Jan 22 '18 at 21:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  umount: /sys/kernel/debug: target is busy.
  
  – msangel
  Aug 4 at 0:34
  

  
  
  
  

add a comment
 | 

3

I had the same problem and this answer helped me to understand the problem a little better.

I've found out that one way to remove the annoying warning is to umount debugfs

mount | grep debugfs 
none on /sys/kernel/debug type debugfs (rw,_netdev)

sudo umount $(mount | grep debugfs | awk 'print $3')

If you now run lsof there is no warning.

share|improve this answer

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this is really why I came looking. I don't care so much why the error is showing up. I really just want it to go away. Thanks damko!
  
  – cjac
  Jan 22 '18 at 21:32
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  umount: /sys/kernel/debug: target is busy.
  
  – msangel
  Aug 4 at 0:34
  

  
  
  
  

add a comment
 | 

I had the same problem and this answer helped me to understand the problem a little better.

I've found out that one way to remove the annoying warning is to umount debugfs

mount | grep debugfs 
none on /sys/kernel/debug type debugfs (rw,_netdev)

sudo umount $(mount | grep debugfs | awk 'print $3')

If you now run lsof there is no warning.

share|improve this answer

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

mount | grep debugfs 
none on /sys/kernel/debug type debugfs (rw,_netdev)

sudo umount $(mount | grep debugfs | awk 'print $3')

share|improve this answer

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

answered Jan 26 '17 at 8:25

damkodamko

13122 bronze badges

2

The issue is that you do not have permission to access the debugfs directory. The tracefs directory was created to allow people to mount the tracing directory directly at /sys/kernel/tracing and not require enabling debugfs. But for backward compatibility, when mounting the debugfs directory, it would automatically mount tracefs in the "tracing" directory of debugfs.

Now when you perform lsof it looks at the /proc/filesystems file as well as /proc/mounts. It sees that tracefs is mounted at /sys/kernel/debug/tracing, and thus tries to stat it. Unfortunately, because /sys/kernel/debug wont let non-root users see inside of it, you get the error message when trying to stat the directory "tracing" from within /sys/kernel/debug. If you unmount the debugfs directory, the warning will go away.

share|improve this answer

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

add a comment
 | 

2

The issue is that you do not have permission to access the debugfs directory. The tracefs directory was created to allow people to mount the tracing directory directly at /sys/kernel/tracing and not require enabling debugfs. But for backward compatibility, when mounting the debugfs directory, it would automatically mount tracefs in the "tracing" directory of debugfs.

Now when you perform lsof it looks at the /proc/filesystems file as well as /proc/mounts. It sees that tracefs is mounted at /sys/kernel/debug/tracing, and thus tries to stat it. Unfortunately, because /sys/kernel/debug wont let non-root users see inside of it, you get the error message when trying to stat the directory "tracing" from within /sys/kernel/debug. If you unmount the debugfs directory, the warning will go away.

share|improve this answer

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

add a comment
 | 

The issue is that you do not have permission to access the debugfs directory. The tracefs directory was created to allow people to mount the tracing directory directly at /sys/kernel/tracing and not require enabling debugfs. But for backward compatibility, when mounting the debugfs directory, it would automatically mount tracefs in the "tracing" directory of debugfs.

Now when you perform lsof it looks at the /proc/filesystems file as well as /proc/mounts. It sees that tracefs is mounted at /sys/kernel/debug/tracing, and thus tries to stat it. Unfortunately, because /sys/kernel/debug wont let non-root users see inside of it, you get the error message when trying to stat the directory "tracing" from within /sys/kernel/debug. If you unmount the debugfs directory, the warning will go away.

share|improve this answer

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

share|improve this answer

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

answered May 29 at 14:05

nevetsnevets

2111 bronze badge

0

The Warning is written to stderr. You can always just redirect this to the /dev/null:

lsof <any-file> 2>/dev/null

Cheers,

share|improve this answer

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

add a comment
 | 

0

The Warning is written to stderr. You can always just redirect this to the /dev/null:

lsof <any-file> 2>/dev/null

Cheers,

share|improve this answer

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

add a comment
 | 

The Warning is written to stderr. You can always just redirect this to the /dev/null:

lsof <any-file> 2>/dev/null

Cheers,

share|improve this answer

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

lsof <any-file> 2>/dev/null

share|improve this answer

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge

answered Apr 30 at 9:35

QuickPrototypeQuickPrototype

10111 bronze badge