linux app read kernel log (klogctl())
2021/5/15 7:27:51
本文主要是介绍linux app read kernel log (klogctl()),对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
linux app read kernel log
man klogctl:
int klogctl(int type, char *bufp, int len);
SYSLOG(2) Linux Programmer's Manual SYSLOG(2) NAME syslog, klogctl - read and/or clear kernel message ring buffer; set console_loglevel SYNOPSIS int syslog(int type, char *bufp, int len); /* No wrapper provided in glibc */ /* The glibc interface */ #include <sys/klog.h> int klogctl(int type, char *bufp, int len); DESCRIPTION Note: Probably, you are looking for the C library function syslog(), which talks to syslogd(8); see syslog(3) for details. This page describes the kernel syslog() system call, which is used to control the kernel printk() buffer; the glibc wrapper function for the system call is called klogctl(). The kernel log buffer The kernel has a cyclic buffer of length LOG_BUF_LEN in which messages given as arguments to the kernel function printk() are stored (regardless of their log level). In early kernels, LOG_BUF_LEN had the value 4096; from kernel 1.3.54, it was 8192; from kernel 2.1.113, it was 16384; since kernel 2.4.23/2.6, the value is a kernel configura- tion option (CONFIG_LOG_BUF_SHIFT, default value dependent on the architecture). Since Linux 2.6.6, the size can be queried with command type 10 (see below). Commands The type argument determines the action taken by this function. The list below specifies the values for type. The symbolic names are defined in the kernel source, but are not exported to user space; you will either need to use the numbers, or define the names yourself. SYSLOG_ACTION_CLOSE (0) Close the log. Currently a NOP. SYSLOG_ACTION_OPEN (1) Open the log. Currently a NOP. SYSLOG_ACTION_READ (2) Read from the log. The call waits until the kernel log buffer is nonempty, and then reads at most len bytes into the buffer pointed to by bufp. The call returns the number of bytes read. Bytes read from the log disappear from the log buffer: the information can be read only once. This is the function executed by the kernel when a user program reads /proc/kmsg. SYSLOG_ACTION_READ_ALL (3) Read all messages remaining in the ring buffer, placing them in the buffer pointed to by bufp. The call reads the last len bytes from the log buffer (nondestructively), but will not read more than was written into the buffer since the last "clear ring buffer" command (see command 5 below)). The call returns the number of bytes read. SYSLOG_ACTION_READ_CLEAR (4) Read and clear all messages remaining in the ring buffer. The call does precisely the same as for a type of 3, but also executes the "clear ring buffer" command. SYSLOG_ACTION_CLEAR (5) The call executes just the "clear ring buffer" command. The bufp and len arguments are ignored. This command does not really clear the ring buffer. Rather, it sets a kernel bookkeeping variable that de- termines the results returned by commands 3 (SYSLOG_ACTION_READ_ALL) and 4 (SYSLOG_ACTION_READ_CLEAR). This command has no effect on commands 2 (SYSLOG_ACTION_READ) and 9 (SYSLOG_ACTION_SIZE_UNREAD). SYSLOG_ACTION_CONSOLE_OFF (6) The command saves the current value of console_loglevel and then sets console_loglevel to minimum_con- sole_loglevel, so that no messages are printed to the console. Before Linux 2.6.32, the command simply sets console_loglevel to minimum_console_loglevel. See the discussion of /proc/sys/kernel/printk, below. The bufp and len arguments are ignored. SYSLOG_ACTION_CONSOLE_ON (7) If a previous SYSLOG_ACTION_CONSOLE_OFF command has been performed, this command restores console_loglevel to the value that was saved by that command. Before Linux 2.6.32, this command simply sets console_loglevel to default_console_loglevel. See the discussion of /proc/sys/kernel/printk, below. The bufp and len arguments are ignored. SYSLOG_ACTION_CONSOLE_LEVEL (8) The call sets console_loglevel to the value given in len, which must be an integer between 1 and 8 (inclu- sive). The kernel silently enforces a minimum value of minimum_console_loglevel for len. See the log level section for details. The bufp argument is ignored. SYSLOG_ACTION_SIZE_UNREAD (9) (since Linux 2.4.10) The call returns the number of bytes currently available to be read from the kernel log buffer via command 2 (SYSLOG_ACTION_READ). The bufp and len arguments are ignored. SYSLOG_ACTION_SIZE_BUFFER (10) (since Linux 2.6.6) This command returns the total size of the kernel log buffer. The bufp and len arguments are ignored. All commands except 3 and 10 require privilege. In Linux kernels before 2.6.37, command types 3 and 10 are allowed to unprivileged processes; since Linux 2.6.37, these commands are allowed to unprivileged processes only if /proc/sys/kernel/dmesg_restrict has the value 0. Before Linux 2.6.37, "privileged" means that the caller has the CAP_SYS_ADMIN capability. Since Linux 2.6.37, "privileged" means that the caller has either the CAP_SYS_ADMIN ca- pability (now deprecated for this purpose) or the (new) CAP_SYSLOG capability.
/* kernel\printk.c */ ... SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len) { return do_syslog(type, buf, len, SYSLOG_FROM_CALL); } ...
这篇关于linux app read kernel log (klogctl())的文章就介绍到这儿,希望我们推荐的文章对大家有所帮助,也希望大家多多支持为之网!
- 2024-12-18git仓库有更新,jenkins 自动触发拉代码怎么配置的?-icode9专业技术文章分享
- 2024-12-18Jenkins webhook 方式怎么配置指定的分支?-icode9专业技术文章分享
- 2024-12-13Linux C++项目实战入门教程
- 2024-12-13Linux C++编程项目实战入门教程
- 2024-12-11Linux部署Scrapy教程:新手入门指南
- 2024-12-11怎么将在本地创建的 Maven 仓库迁移到 Linux 服务器上?-icode9专业技术文章分享
- 2024-12-10Linux常用命令
- 2024-12-06谁看谁服! Linux 创始人对于进程和线程的理解是…
- 2024-12-04操作系统教程:新手入门及初级技巧详解
- 2024-12-04操作系统入门:新手必学指南