内核的输出级别和printk的输出级别
printk函数时具有打印级别,级别0-7,数字越小,级别越高
内核也有默认的输出级别
内核也有默认的输出级别
让我们来测试一下
#include <linux/init.h> #include <linux/module.h> MODULE_LICENSE("GPL v2"); int __init printk_init(void) { printk("<0>""printk level 0!\n"); printk("<1>""printk level 1!\n"); printk("<2>""printk level 2!\n"); printk("<3>""printk level 3!\n"); printk("<4>""printk level 4!\n"); printk("<5>""printk level 5!\n"); printk("<6>""printk level 6!\n"); printk("<7>""printk level 7!\n"); printk("printk no level!\n"); return 0; } void __exit printk_exit(void) { printk("<0>""printk level 0!\n"); printk("<1>""printk level 1!\n"); printk("<2>""printk level 2!\n"); printk("<3>""printk level 3!\n"); printk("<4>""printk level 4!\n"); printk("<5>""printk level 5!\n"); printk("<6>""printk level 6!\n"); printk("<7>""printk level 7!\n"); printk("printk no level!\n"); } module_init(printk_init); module_exit(printk_exit);
当printk的输出级别小于内核的输出级别时,printk打印的内容就可以被打印出来。否则printk的打印信息将被忽略
查看内核的输出级别
cat /proc/sys/kernel/printk7 4 1 7
修改方法
方法1:
echo 5 > /proc/sys/kernel/printk
缺点:方法1无法修改在内核启动时的输出信息
方法2:
通过uboot的环境变量bootargs传递打印级别的参数
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 debug //级别为10
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 quiet //级别为4
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 loglevel=6 //直接指定级别
echo 5 > /proc/sys/kernel/printk
缺点:方法1无法修改在内核启动时的输出信息
方法2:
通过uboot的环境变量bootargs传递打印级别的参数
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 debug //级别为10
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 quiet //级别为4
set bootargs root=/dev/nfs init=/linuxrc nfsroot=192.168.1.141:/home/student/workdir/rootfs ip=192.168.1.20:192.168.1.141:192.168.1.1:255.255.255.0::eth0:on console=ttySAC0,115200 loglevel=6 //直接指定级别