Linux Log Management commands

Linux Log Management command details log is very important for security. It records various events that occur in the system every day. You can use it to check the cause of the error, or the traces left by the attacker during the attack. The main functions of logs are audit and monitoring. It can also monitor the system status in real time, monitor and track intrusions, and so on. In Linux, there are three major log subsystems: connection time logs-executed by multiple programs, write records to programs such as/var/log/wtmp and/var/run/utmp and login to update the wtmp and utmp files so that the system administrator can track who is logged on to the system at any time. Process statistics-executed by the system kernel. When a process terminates, each process writes a record to the process Statistics file (pacct or acct. Process statistics are used to provide command usage statistics for basic services in the system. Error Log -- executed by syslogd. Various system Daemon Processes, user programs, and kernels report noteworthy events to files/var/log/messages through syslog. In addition, many UNIX programs create logs. Servers that provide network services such as HTTP and FTP also maintain detailed logs. Common log files are as follows: access-log record HTTP/web transmission acct/pacct record USER command aculog record MODEM activity btmp record failure record lastlog record recent successful login events and last unsuccessful log on to messages to record information from syslog (some links to the syslog file) sudolog records the use of sudo commands sulog records the use of syslogs using the su command to record information from syslogs (usually linked to the messages file) utmp records the number of currently logged-on users (wtmp) each user (permanent records of entry and exit times) xferlog records FTP session (utmp), wtmp, and lastlog files are the key for most UNIX log subsystems to be reused-maintain user Logon entry and exit records. The information about the current logon user is recorded in the file utmp; the logon entry and exit records are recorded in the file wtmp; the last logon file can be viewed using the lastlog command. Data exchange, shutdown, and restart are also recorded in the wtmp file. All records contain timestamps. These files (lastlog is usually not large) grow rapidly in systems with a large number of users. For example, the wtmp file can grow infinitely unless it is intercepted regularly. Many systems configure wtmp to be used cyclically in units of one day or one week. It is usually modified by the script run by cron. These scripts are renamed and the wtmp file is recycled. Generally, wtmp is named wtmp.1 after the first day, wtmp.1 is changed to wtmp.2 after the second day, and so on until wtmp.7. Each time a user logs on, the login program checks the user's UID in the lastlog file. If the logon time is found, the user's Last Logon Time, exit time, and host name are written to the standard output, and the login program records the new Logon Time in lastlog. After a new lastlog is written, the utmp file is opened and the user's utmp record is inserted. This record is always used when a user logs on and exits. The utmp file is used by various command files, including who, w, users, and finger. Next, the login program opens the file wtmp and appends the user's utmp record. When a user logs on and exits, the same utmp record with the updated timestamp is appended to the file. The wtmp file is used by the program last and ac. The specific command wtmp and utmp files are binary files, and they cannot be cut or merged by such tail commands (using cat commands ). You need to use the information contained in the two files by who, w, users, last, and ac. Who: The who command queries the utmp file and reports to each user currently logged on. The default output of Who includes the user name, terminal type, logon date, and remote host. For example: who (Press ENTER) display: chyang pts/0 Aug 18 ynguo pts/2 Aug 18 ynguo pts/3 Aug 18 lewis pts/4 Aug 18 ynguo pts/7 Aug 18 ylou pts/8 Aug if the wtmp file name is specified, then, the who command queries all previous records. The command who/var/log/wtmp will report every login since the wtmp file was created or deleted. The w: w command queries the utmp file and displays information about each user in the current system and the processes it runs. Example: w (Press ENTER): 3: 36pm up 1 day, 6 users, load average: 0.23, 0.29, 0.27. User tty from login @ idle jcpu pcpu what chyang pts/0 202.38.68.242 pm 0.08 s 0.04 s-bash ynguo pts/2 202.38.79.47 pm 0.00 s 0.14 s 0.05 w lewis pts/3 202.38.64.233 :55 pm 30: 39 0.27 s 0.22 s-bash lewis pts/4 202.38.64.233 pm 6.00 s 4.03 s 0.01 s sh/home/users/ynguo pts/7 simba. nic. ustc. e pm 0.00 s 0.47 s 0.24 s telnet mail ylou pts/8 202.38.64.235 pm 1: 09 m 0.10 s 0.04 s-bash users: Users prints the current logon user with a single line. Each displayed user name corresponds to a logon session. If a user has more than one login session, the user name will display the same number of times. For example, users (Press ENTER) shows: chyang lewis ylou ynguo last: last Command searches back for wtmp to show users who have logged on since the first file creation. Example: chyang pts/9 202.38.68.242 Tue Aug 1-() cfan pts/6 202.38.64.20.tue Aug 1) chyang pts/4 202.38.68.242 Tue Aug 1-() lewis pts/3 202.38.64.233 Tue Aug 1) lewis pts/2 202.38.64.233 Tue Aug 1-() if the user is specified, only recent activities of the user are reported last time. For example: last ynguo (Press ENTER: ynguo pts/4 simba. nic. ustc. e Fri Aug 4 -() Ynguo pts/4 simba. nic. ustc. e Thu Aug 3-() ynguo pts/11 simba. nic. ustc. e Thu Aug 3-() ynguo pts/0 simba. nic. ustc. e Thu Aug 3-() ynguo pts/0 simba. nic. ustc. e Wed Aug 2 0:04-0:16 1 + 02: 12) ynguo pts/0 simba. nic. ustc. e Wed Aug 2 00:43-00:54 (00:11) ynguo pts/9 simba. nic. ustc. e Thu Aug 1-() Syslog device Syslog has been adopted by many log functions. Among multiple protection measures-any program can log events through syslog. Syslog records system events, writes to a file or device, or sends a message to users. It can record local events or events on another host through the network. The Syslog device depends on two important files:/etc/syslogd (Daemon) and/etc/syslog. conf configuration file. Traditionally, most syslog information is written to the/var/adm or the/var/log directory information file (messages. *). A typical syslog record includes the name of the generated program and a text message. It also includes a device and a priority range (but not in the day ). Each syslog message is assigned to one of the following main devices: LOG_AUTH -- Authentication System: login, su, getty, and other LOG_AUTHPRIV -- same as LOG_AUTH, but only log on to the LOG_CRON -- cron daemon in the selected file that is readable to a single user -- Other System daemon, such as routed LOG_FTP -- File Transfer Protocol: ftpd, tftpd LOG_KERN -- kernel-generated message LOG_LPR -- System printer Buffer Pool: lpr, lpd LOG_MAIL -- email system LOG_NEWS -- network news system LOG_SYSLOG -- by syslogd (8) generated internal message LOG_USER -- the message LOG_UUCP--UUCP subsystem LOG_LOCAL0 ~ generated by the random user process ~ LOG_LOCAL7 -- give a few different priorities for each event for local use of retained Syslog: LOG_EMERG-Emergency LOG_ALERT-problems that should be corrected immediately, such as system database damage LOG_CR99v-important situations, for example, a hard drive error LOG_ERR -- error LOG_WARNING -- warning message LOG_NOTICE -- is not an error, but you may need to handle LOG_INFO -- intelligence information LOG_DEBUG -- contains intelligence information, which is usually intended to use syslog when debugging a program. the conf file specifies the Log action recorded by the syslogd program, which queries the configuration file at startup. This file consists of a single entry of different programs or message categories, each occupying a row. Provides a selection domain and an action domain for each type of message. These fields are separated by tabs: select a domain to specify the type and priority of the message. The action domain indicates the action that syslogd performs when receiving a message that matches the selection criteria. Each option is composed of a device and a priority. When a priority is specified, syslogd records a message with the same or higher priority. Therefore, if "crit" is specified, all messages marked as crit, alert, and emerg will be recorded. The action fields in each row indicate where to send a specified message to the selected domain. For example, if you want to record all the mail messages to a file, Log all the mail messages in one place mail. */var/log/maillog other devices also have their own logs. UUCP and news devices can produce many external messages. It stores these messages in its own logs (/var/log/spooler) and limits the level to "err" or higher. Example: # Save mail and news errors of level err and higher in aspecial file. uucp, news. crit/var/log/spooler when an emergency message arrives, all users may want to get it. You may also want to receive and save your own logs. # Everybody gets emergency messages, plus log them on anther machine *. emerg **. emerg @ linuxaid.com.cn alert message should be written to the personal account of root and tiger: # Root and Tiger get alert and higher messages *. alert root, tiger sometimes syslogd will generate a large number of messages. For example, the kernel ("kern" device) may be lengthy. You may want to record kernel messages to/dev/console. The following example shows that the kernel Log record has been commented out: # Log all kernel messages to the console # Logging much else clutters up the screen # kern. */dev/con