Re: Please help me to resolve a tail related server fault

[Liu Haifeng]

I don't think tail would die at that point. I have tested this:

tail -F a.log

#after eof

rm a.log

#tail then gives an error,but still waiting

#after a while I run

echo hello > a.log

#here tail functions continuously

在 2013-2-8，下午11:01，Cryptographrix <address@hidden> 写道：

If it's happening when some type of log rotation rotates the log out, there is a good possibility that tail catches the EOF when log rotation kicks the process that created the file and tail dies.

I believe the retry feature of tail may not necessarily retry after what it sees as an EOF, and that would probably be intentional.

To test this, you can tail the file yourself when log rotation is going to run.  If you go back to shell, then you need to write a retry into the Java code you're writing to compensate.

It may very likely be that Oracle added STDIN limitations into Java with the latest releases as well.

On Feb 8, 2013 9:36 AM, "Liu Haifeng" <address@hidden> wrote:

We are developing our own tailer now, but I want to find out what happened with gnu tail or oracle java.

On Feb 8, 2013, at 10:03 PM, Cryptographrix <address@hidden> wrote:

I do not know what limitations STDIN has on it in java offhand, but it sounds like this is what you are trying to do:

http://www.informit.com/guides/content.aspx?g=java&seqNum=226

On Thu, Feb 7, 2013 at 11:52 PM, Liu Haifeng <address@hidden> wrote:

Hi

I have a log transport agent written in java which creates a sub process that executing "tail -F a.log" to tail log file,and the output is piped to the main java process,thus I can read and transport log content using java.

This worked fine in the past 30 days,but now it seams the java process can't read any data. I checked java thread stack, it's blocked on Java.io.FileInputStream.readBytes.

The log file I am tailing is rotated every one hour,and the fault happened at the moment the rotating script is supposed to run.

Currently I have no idea about this fault. Here following by some status of the tail process, not more as I don't have the root privilege.

 

#cat /proc/28195/status

 

Name:   tail

State:  S (sleeping)

SleepAVG:       78%

Tgid:   28195

Pid:    28195

PPid:   28143

TracerPid:      0

Uid:    0       0       0       0

Gid:    0       0       0       0

FDSize: 256

Groups: 0 1 2 3 4 6 10

VmPeak:     3828 kB

VmSize:     3828 kB

VmLck:         0 kB

VmHWM:       524 kB

VmRSS:       524 kB

VmData:      180 kB

VmStk:        88 kB

VmExe:        36 kB

VmLib:      1468 kB

VmPTE:        36 kB

StaBrk: 198b3000 kB

Brk:    198d4000 kB

StaStk: 7fff7679c1d0 kB

Threads:        1

SigQ:   0/32768

SigPnd: 0000000000000000

ShdPnd: 0000000000000000

SigBlk: 0000000000000004

SigIgn: 0000000000000003

SigCgt: 0000000000000000

CapInh: 0000000000000000

CapPrm: 00000000fffffeff

CapEff: 00000000fffffeff

Cpus_allowed:  00000000,00000000,00000000,00000000,00000000,00000000,ffffffff,ffffffff

Mems_allowed:   00000000,00000001

 

#cat /proc/28195/stat

28195 (tail) S 28143 28138 27881 0 -14202496 141 0 1 0 10328 53939 0 0 18 0 1 0 214643641 3919872 131 18446744073709551615 1 1 0 0 0 0 4 3 0 18446744073709551615 0 0 17 2 0 0 1

 

#yum list|grep coreutils

coreutils.x86_64                           5.97-34.el5_8.1             installed

policycoreutils.x86_64                     1.33.12-14.8.el5            installed

policycoreutils-gui.x86_64                 1.33.12-14.8.el5            base

policycoreutils-newrole.x86_64             1.33.12-14.8.el5            base