Questions tagged [logs]

Configuring or analysing log files (text files where programs output error and informational messages, useful for debugging and troubleshooting).

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436
votes
4answers
588k views

How to see full log from systemctl status service?

I check service status with systemctl status service-name. By default, I see few rows only, so I add -n50 to see more. Sometimes, I want to see full log, from start. It could have 1000s of rows. Now,...
204
votes
2answers
284k views

View stdout/stderr of systemd service

I have created a simple systemd service file for a custom application. The application works well when I run it manually, but my CPU gets maxed out when I run it with systemd. I'm trying do track ...
189
votes
4answers
796k views

Where are Apache file access logs stored?

Does anyone know where file access logs are stored, so I can run a tail -f command in order to see who is accessing a particular file. I have XAMPP, which is an Apache server installed on my machine, ...
184
votes
10answers
409k views

Where are cron errors logged?

If I setup cron jobs incorrectly they appear to silently fail. Where should I look for an error log to understand what went wrong?
173
votes
1answer
503k views

How to clean log file? [duplicate]

Is there a better way to clean the log file? I usually delete the old logfile and create a new logfile and I am looking for a shorter type/bash/command program. How can I use an alias?
157
votes
7answers
168k views

How can I see dmesg output as it changes?

I'm writing a device driver that prints error message into ring buffer dmesg output. I want to see the output of dmesg as it changes. How can I do this?
127
votes
3answers
243k views

Find and remove large files that are open but have been deleted

How does one find large files that have been deleted but are still open in an application? How can one remove such a file, even though a process has it open? The situation is that we are running a ...
126
votes
11answers
450k views

How to find out from the logs what caused system shutdown?

E.g. I'm seeing this in /var/log/messages: Mar 01 23:12:34 hostname shutdown: shutting down for system halt Is there a way to find out what caused the shutdown? E.g. was it run from console, or ...
121
votes
5answers
332k views

How to monitor only the last n lines of a log file?

I have a growing log file for which I want to display only the last 15 lines. Here is what I know I can do: tail -n 15 -F mylogfile.txt As the log file is filled, tail appends the last lines to the ...
112
votes
1answer
37k views

How to do a `tail -f` of log rotated files?

On a long running system I usually have a terminal with $ tail -f /var/log/kern.log or something like this open. But from time to time I have to restart such command because no new messages are ...
91
votes
3answers
202k views

what is the CentOS equivalent of /var/log/syslog (on Ubuntu)?

On ubuntu this file exists: /var/log/syslog. However the same file does not appear on CentOS Distributions. What is the equivalent file on CentOS?
65
votes
5answers
143k views

Where are my sshd logs?

I can't find my sshd logs in the standard places. What I've tried: Not in /var/log/auth.log Not in /var/log/secure Did a system search for 'auth.log' and found nothing I've set /etc/ssh/sshd_config ...
64
votes
7answers
289k views

Logging SSH access attempts

I've configured an ubuntu server with openssh in order to connect to it and execute commands from a remote system like a phone or a laptop. The problem is... I'm probably not the only one. Is there ...
64
votes
3answers
57k views

grep inside less?

I'm currently sifting through a lot of unfamiliar logs looking for some issues. The first file I look at is Events.log, and I get at least three pages in less which appear to display the same event ...
63
votes
3answers
39k views

Observe multiple log files in one output

Is there an easy way to do something like tail -f mylogfile but to have the changes of more than one file displayed (maybe with the file name added as prefix to each line)? Or maybe a GUI tool? I am ...
63
votes
7answers
55k views

Can I find out which ssh key was used to access an account?

Is it possible to find out which ssh key was used to access an account? I have an account on a server that I let several (trusted!) people have access to via ssh. I'd find it useful to be able to ...
60
votes
8answers
135k views

Meaning of “Connection closed by xxx [preauth]” in sshd logs

We have a Windows batch script, which connects automatically to a linux server via PLINK (putty). There is NO public private key authentication, the user and the password are in the script. On our ...
57
votes
4answers
158k views

What's the difference of dmesg output and /var/log/messages?

AFAIK dmesg shows information about kernel and kernel modules, and /var/log/messages also shows information produced by kernel and modules. So what's the difference? Does /var/log/messages ⊂ output ...
56
votes
6answers
79k views

Best way to follow a log and execute a command when some text appears in the log

I have a server log that outputs a specific line of text into its log file when the server is up. I want to execute a command once the server is up, and hence do something like the following: tail -f ...
56
votes
5answers
26k views

monitor files (à la tail -f) in an entire directory (even new ones)

I normally watch many logs in a directory doing tail -f directory/*. The problem is that a new log is created after that, it will not show in the screen (because * was expanded already). Is there a ...
50
votes
5answers
37k views

How can I write to dmesg from command line?

I'd like to write a statement to dmesg. [How] can I do this?
47
votes
8answers
191k views

History of IP addresses that accessed a server via ssh

It has come to my attention that a server of mine has been hacked and infected with a known Chinese botnet. It was a prototype/testing virtual machine with its own static IP(US address) so no harm ...
45
votes
8answers
76k views

How to find which process is regularly writing to disk?

How can I find which process is constantly writing to disk? I like my workstation to be close to silent and I just build a new system (P8B75-M + Core i5 3450s -- the 's' because it has a lower max ...
45
votes
2answers
98k views

Debug out-of-memory with /var/log/messages

The following report is thrown in my messages log: kernel: Out of memory: Kill process 9163 (mysqld) score 511 or sacrifice child kernel: Killed process 9163, UID 27, (mysqld) total-vm:2457368kB, ...
42
votes
1answer
163k views

Where to find the Crontab logs in CentOS

First of all I'm using CentOS [root@a etc]# cat system-release CentOS release 6.5 (Final) [root@a cron.daily]# ps -ef | grep cron root 982 1 0 Jun14 ? 00:01:15 crond root ...
41
votes
2answers
28k views

What are the concepts of “kernel ring buffer”, “user level”, “log level”?

I often saw the words "kernel ring buffer", "user level", "log level" and some other words appear together. e.g. /var/log/dmesg Contains kernel ring buffer information. /var/log/kern.log ...
35
votes
4answers
26k views

Is there an equivalent of GNU Screen's “log” command in tmux?

I make heavy use of screen's "log" command to log the output of a session to a file, when I am making changes in a given environment. I searched through tmux's man page, but couldn't find an ...
34
votes
2answers
40k views

How to get the output inside `screen` out to a script?

I have a screen instance running, and I would need to execute some code inside the screen, and get the result out to my script. The first part is quite easy, I just screen -S session_name -X eval '...
33
votes
2answers
16k views

Record every keystroke and store in a file

I need to record every keystroke and store in a file in the user directory ~, when using my account, I am not sudoer and I cannot install programs (like logKeys) in any way. How could I do so using ...
33
votes
3answers
54k views

Where can I see a list of kernel killed processes?

Is there some way I can check which of my processes the kernel has killed? Sometimes I log onto my server and find that something that should've run all night just stopped 8 hours in and I'm unsure if ...
32
votes
6answers
53k views

How do I add newlines between lines printed on the command line?

Mail logs are incredibly difficult to read. How could I output a blank line between each line printed on the command line? For example, say I'm grep-ing the log. That way, multiple wrapped lines aren'...
32
votes
3answers
84k views

Where are sudo incidents logged?

When someone is not in the sudoers group and try to use sudo, get an error message like this one: yzT is not in the sudoers file. This incident will be reported. I'm trying to figure out in which ...
32
votes
3answers
20k views

How to redirect stderr and stdout to different files and also display in terminal?

I want to see the output of a command in the terminal as if there was no redirection. Also, stderr needs to be redirected to err.log and stdout needs to be redirected to stdout.log. It would be nice ...
30
votes
4answers
14k views

Where are userspace programs supposed to save their logs?

I am writing a script that I want to run without privileges. I want the errors that the script encounters to be logged to some log file. I do not not have privileges to write one to /var/log. And I do ...
29
votes
2answers
66k views

Using exec and tee to redirect logs to stdout and a log file in the same time [duplicate]

In a bash script, how can I redirect all standard outputs to a log file and tee the output on the screen using exec ? log_file="$HOME/logs/install.txt-`date +'%Y-%m-%d_%H-%M-%S'`" [ -f "$log_file" ] |...
29
votes
4answers
10k views

How to do a continous 'wc -l' with gnu texttools?

I know of course that cat logfile.txt | wc -l 120 will tell me the number of lines in a file. Whereas tail -f logfile.txt will show me the new lines that another program writes to logfile.txt. ...
29
votes
2answers
64k views

Cron log on debian systems

On Redhat systems cron logs into /var/log/cron file. What is the equivalent of that file on Debian systems?
27
votes
2answers
33k views

add new syslog facility

I would like to use syslog to log messages coming from my PHP based site. My question is - can I add custom facility name? I know there are predefined facilities like: auth, authpriv, cron, dæmon, ...
27
votes
2answers
44k views

In which log should I check for udev errors?

I've written a udev rule which is run each time my device is mounted/dismounted. However, in which Linux (Debian) error log should I check when debugging such rules?
24
votes
3answers
9k views

How do I find the line number in Bash when an error occured?

How do you find the line number in Bash where an error occurred? Example I create the following simple script with line numbers to explain what we need. The script will copy files from cp $file1 $...
24
votes
6answers
13k views

How keep last 50 lines in logfile

I try to keep last 50 lines in my file where I save temperature every minute. I used this command: tail -n 50 /home/pi/Documents/test > /home/pi/Documents/test But the result is empty test file. ...
24
votes
7answers
41k views

tail -f, but with line numbers

I'm trying to see how many times foo bar appears in /var/log/foo.log within an arbitrary amount of time on a remote server, but nothing that I've tried so far has worked. I've already got a timer ...
24
votes
9answers
54k views

Command to display first few and last few lines of a file

I have a file with many rows, and each row has a timestamp at the starting, like [Thread-3] (21/09/12 06:17:38:672) logged message from code..... So, I frequently check 2 things from this log file. ...
23
votes
7answers
40k views

How do you keep only the last n lines of a log file?

A script I wrote does something and, at the end, appends some lines to its own logfile. I'd like to keep only the last n lines (say, 1000 lines) of the logfile. This can be done at the end of the ...
23
votes
2answers
32k views

How to get last crash log from ArchLInux

My system suddenly crashed, I have restart it, where could I find the last/previous crash log, since there are no /var/log/syslog* anymore..
23
votes
1answer
21k views

Listening for journalctl changes

Usually I use tail -f /var/log/messages to get updates if there are new lines. How to have the similar functionality for journalctl?
23
votes
5answers
49k views

How can I track who SSH'es into my linux machine?

I'm running Ubuntu 10.04. Is there a way I can get a daily report of who has logged onto the box, what time, and even - this may be asking too much - a report of the commands they used? This is a low-...
23
votes
1answer
8k views

Hide lines based on multiple patterns

I'm using less to view log files quite a lot and every so often I'd like to filter the output by hiding lines which contains some keywords. In less it's possible to filter-out lines with &!<...
22
votes
4answers
50k views

make a log file

Is there any way to make a log file for maintaining some data in /var/log/ with the help of some library function or system call in c language in linux. And I also want to know the standards that we ...
21
votes
4answers
35k views

View only the new entries in a growing log file

tail -f x.log I use this command to see a growing log file in the command prompt. I am interested only in seeing the log lines that are written to the file after running tail -f and not interested ...

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