Red Hat ENTERPRISE LINUX 5.4 - SYSTEMTAP BEGINNERS GUIDE Informations techniques télécharger pdf (Page 105)

Kernel Probes 91

6.4.1 How to List Registered Kernel

Probes

The list of all currently registered kprobes is in the /sys/kernel/de

bug/kprobes/list file.

saturn.example.com:~ # cat /sys/kernel/debug/kprobes/list

c015d71a k vfs_read+0x0 [DISABLED]

c011a316 j do_fork+0x0

c03dedc5 r tcp_v4_rcv+0x0

The first column lists the address in the kernel where the probe is inserted. The sec-

ond column prints the type of the probe: k for kprobe, j for jprobe, and r for return

probe. The third column specifies the symbol, offset and optional module name of the

probe. The following optional columns include the status information of the probe. If

the probe is inserted on a virtual address which is not valid anymore, it is marked with

[GONE]. If the probe is temporarily disabled, it is marked with [DISABLED].

6.4.2 How to Switch All Kernel Probes On

or Off

The /sys/kernel/debug/kprobes/enabled file represents a switch with

which you can globally and forcibly turn on or off all the registered kernel probes. To

turn them off, simply enter

echo "0" > /sys/kernel/debug/kprobes/enabled

on the command line as root. To turn them on again, enter

echo "1" > /sys/kernel/debug/kprobes/enabled

Note that this way you do not change the status of the probes. If a probe is temporari-

ly disabled, it will not be enabled automatically but will remain in the [DISABLED]

state after entering the latter command.

6.5 For More Information

To learn more about kernel probes, look at the following sources of information:

1 2 ... 100 101 102 103 104 105 106 107 108 109 110 ... 239 240

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Red Hat ENTERPRISE LINUX 5.4 - SYSTEMTAP BEGINNERS GUIDE Informations techniques Page 105