Mixing
Debug messages not being printed on the console
I am trying to enable printing the debug messages on the console.
#include <linux/kernel.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");
static int test_hello_init(void)
{
printk(KERN_INFO"%s: In initn", __func__);
return 0;
}
static void test_hello_exit(void)
{
printk(KERN_INFO"%s: In exitn", __func__);
}
module_init(test_hello_init);
module_exit(test_hello_exit);
To get the Info messages on the console, i executed the following command: dmesg -n7
cat /proc/sys/kernel/printk
7 4 1 7
When I load the module using insmod, i don't get any message on the terminal, while it is available when I type dmesg. What mistake i am making here.
linux linux-kernel linux-device-driver
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
add a comment |
I am trying to enable printing the debug messages on the console.
#include <linux/kernel.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");
static int test_hello_init(void)
{
printk(KERN_INFO"%s: In initn", __func__);
return 0;
}
static void test_hello_exit(void)
{
printk(KERN_INFO"%s: In exitn", __func__);
}
module_init(test_hello_init);
module_exit(test_hello_exit);
To get the Info messages on the console, i executed the following command: dmesg -n7
cat /proc/sys/kernel/printk
7 4 1 7
When I load the module using insmod, i don't get any message on the terminal, while it is available when I type dmesg. What mistake i am making here.
linux linux-kernel linux-device-driver
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
add a comment |
I am trying to enable printing the debug messages on the console.
#include <linux/kernel.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");
static int test_hello_init(void)
{
printk(KERN_INFO"%s: In initn", __func__);
return 0;
}
static void test_hello_exit(void)
{
printk(KERN_INFO"%s: In exitn", __func__);
}
module_init(test_hello_init);
module_exit(test_hello_exit);
To get the Info messages on the console, i executed the following command: dmesg -n7
cat /proc/sys/kernel/printk
7 4 1 7
When I load the module using insmod, i don't get any message on the terminal, while it is available when I type dmesg. What mistake i am making here.
linux linux-kernel linux-device-driver
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
I am trying to enable printing the debug messages on the console.
#include <linux/kernel.h>
#include <linux/module.h>
MODULE_LICENSE("GPL");
static int test_hello_init(void)
{
printk(KERN_INFO"%s: In initn", __func__);
return 0;
}
static void test_hello_exit(void)
{
printk(KERN_INFO"%s: In exitn", __func__);
}
module_init(test_hello_init);
module_exit(test_hello_exit);
To get the Info messages on the console, i executed the following command: dmesg -n7
cat /proc/sys/kernel/printk
7 4 1 7
When I load the module using insmod, i don't get any message on the terminal, while it is available when I type dmesg. What mistake i am making here.
linux linux-kernel linux-device-driver
linux linux-kernel linux-device-driver
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
asked Jan 1 at 13:20
md.jamalmd.jamal
476520
476520
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
Messages from kernel are not printed on terminal (unless it's specified as console= in kernel cmdline). They are appended to kernel log, which exists in kernel. It's accessible to user space programs via device file /dev/kmsg. This file is read by dmesg command in order to print kernel log content on terminal.
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.virsh console) thenconsole=ttyS0should work fine.
– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should useconsole=tty0.
– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
|
show 4 more comments
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Messages from kernel are not printed on terminal (unless it's specified as console= in kernel cmdline). They are appended to kernel log, which exists in kernel. It's accessible to user space programs via device file /dev/kmsg. This file is read by dmesg command in order to print kernel log content on terminal.
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.virsh console) thenconsole=ttyS0should work fine.
– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should useconsole=tty0.
– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
|
show 4 more comments
Messages from kernel are not printed on terminal (unless it's specified as console= in kernel cmdline). They are appended to kernel log, which exists in kernel. It's accessible to user space programs via device file /dev/kmsg. This file is read by dmesg command in order to print kernel log content on terminal.
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.virsh console) thenconsole=ttyS0should work fine.
– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should useconsole=tty0.
– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
|
show 4 more comments
Messages from kernel are not printed on terminal (unless it's specified as console= in kernel cmdline). They are appended to kernel log, which exists in kernel. It's accessible to user space programs via device file /dev/kmsg. This file is read by dmesg command in order to print kernel log content on terminal.
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
Messages from kernel are not printed on terminal (unless it's specified as console= in kernel cmdline). They are appended to kernel log, which exists in kernel. It's accessible to user space programs via device file /dev/kmsg. This file is read by dmesg command in order to print kernel log content on terminal.
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
answered Jan 1 at 13:57
Robert BaldygaRobert Baldyga
7715
7715
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.virsh console) thenconsole=ttyS0should work fine.
– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should useconsole=tty0.
– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
|
show 4 more comments
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.virsh console) thenconsole=ttyS0should work fine.
– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should useconsole=tty0.
– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
what should be the value of console field in ubuntu machine running on VM
– md.jamal
Jan 1 at 14:35
If you are using serial console (e.g.
virsh console) then console=ttyS0 should work fine.– Robert Baldyga
Jan 1 at 14:58
If you are using serial console (e.g.
virsh console) then console=ttyS0 should work fine.– Robert Baldyga
Jan 1 at 14:58
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
No. I am not using serial console. I want messages to be displayed on terminal
– md.jamal
Jan 1 at 15:00
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should use
console=tty0.– Robert Baldyga
Jan 1 at 15:10
By " terminal" you mean QEMU monitor? If yes, then, as it's regular VT, so you should use
console=tty0.– Robert Baldyga
Jan 1 at 15:10
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
The one we use after typing CTRL+ALT+T, did not work after adding console=tty0, my command line: BOOT_IMAGE=/boot/vmlinuz-4.19.6 root=UUID=c17d5f82-e020-4ded-a082-89fd7e54d893 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US sysrq_always_enablde nokaslr console=tty0
– md.jamal
Jan 1 at 15:26
|
show 4 more comments
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