Questions tagged [strace]
The strace tag has no usage guidance.
86
questions
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how to see the verbose output of a process that is running that writes to a file (shred)
I am running the shred command to securely wipe some storage.
I would like to see its progress, but have lost the ssh terminal that was running the command.
Is there a way that I can use to see the ...
0
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0
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44
views
Why server response time is more than a minute for a website, it happens for one website and other website loads fine?
I have multiple websites hosted on this server and one website "server response time" is very very high (more than a minute).
below are the findings... and i am unable to understand whats ...
0
votes
1
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346
views
memcached causes Apache processes to hang indefinitely
I have been tracking down the source of Apache processes hanging indefinitely. Unfortunately, I need to regularly reboot Apache as it eventually exhausts all slots. The Apache status page below shows ...
- 51
0
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1
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218
views
Dump client ssh key from server side
To investigate on some issue, I need to dump the full ssh key offered by the ssh client to the ssh server.
Up to this point, I tried to
put the parent of all sshd server (belongs to root) LogLevel to ...
- 103
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0
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901
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WSL PING "system error"
I have a weird PING error in WSL2, Ubuntu 20.04 distribution.
When I'm doing nslookup - all ok:
root@i:~# nslookup google.com
Server: 172.19.224.1
Address: 172.19.224.1#53
Non-...
- 3
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1k
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Dovecot cannot read TLS certificate
On my CentOS 7 system I am trying to run dovecot with TLS required.
For that, I created my private key and certificate in
[root@homeserver /]# ls -lZ indernet/cert/homeserver.*
-r--r--r--. root ...
- 133
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359
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read system call freeze
I have a VPS which sometimes suddenly got stuck. Recently I found ssh session will get stuck when I run ps aux. After run strace ps aux I got below.
stat("/proc/1573", {st_mode=S_IFDIR|0555, ...
- 11
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45
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What's the best approach to find out in doing what a Linux OS process is stuck?
Oracle DBA here! No experience at all in troubleshooting Linux performance...
I need to identify the bottleneck in an Oracle database running on Oracle Linux. The same procedure runs fine on other VMs,...
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335
views
How to configure nginx better to reduce redundant system calls when APIs are called?
I have a Laravel application running in production, and there are a few APIs that used a lot. Something was creating a bottleneck and it used to stall our servers (3 with Load Balancer). After ...
- 135
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2
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275
views
Simple command to display in terminal the network activity of a command? A better formatted strace?
I want to debug a program which makes a simple network connection.
Is there any command which will print the network activity of a command, something that will show me (e.g. in a hexdump) what is ...
- 31.9k
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400
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Record SSH commands sent to a Mac from Windows
I've got a bit of a puzzler - I am an administrator on both a Windows 10 and a Mac Catalina machine.
The Windows machine is currently running software that has a known bug - SSH commands are sent to ...
- 53
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571
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High httpd CPU usage, server load, strace is stuck
I'm runnning Directadmin with apache2 and MariaDB server. But I'm having a hard time to understand why my server's CPU usage is so high.
htop screenshot
When I try to look what is happening with ...
- 21
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293
views
Trace httpd when using cgi
I have configured httpd (apache2.4.6) cgi to run /bin/bash scripts.
I would like to trace httpd calls of /bin/bash and see the actual command that is run.
So far I have tried to use strace -p but for ...
- 13
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186
views
How to use strace to monitor files being saved on an smb share or being transferred over http
Can strace be used to trigger events or notify whenever a file is saved on an smb share or file is uploaded to a website over http/https?
- 227
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1k
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Debugging slow ls on cifs mount strace makes it fast
I've got a server that has a cifs share (Azure storage files) mounted. Sometimes ls is returning slowly (20seconds). After debugging a bit I've so far found that:
doing ls /data/some/symlink/...
- 171
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500
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Stack trace of mount command shows File not found error
When I run a program, I am getting a mount error:
[root@host ~]# ip vrf exec wan1 /usr/sbin/ssh [email protected]
Failed to mount cgroup2: No such file or directory
I know my kernel supports cgroup2:
[...
- 51
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38
views
Select waiting on what?
I have a python 2.7 app running on RHEL 6 that occasionally hangs. If I strace the app, I get this repeatedly:
[pid 180442] select(0, NULL, NULL, NULL, {10, 0}) = 0 (Timeout)
[pid 180442] select(0, ...
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4
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1
answer
2k
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What might be causing repeated mmap/munmap in strace results?
I have a (node.js) application which is occasionally causing 100% CPU usage. I've attached to the process with strace when it's been in this state - but I don't know what to make if the strace output....
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2
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2
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1k
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Centos 6 vs Centos 7 file access performance [closed]
I'd like some assistance in trying to figure out what could explain Centos 7 being slower in accessing a file then Centos 6. It's about a 17% difference.
Here's a simple test:
[root@test-centos6 shm]...
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2k
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Debugging slow wordpress site with strace
I'm trying to get to the bottom of a wordpress site that runs very slowly: on requesting a page, it hangs for around 20 seconds before the page starts to load.
I've tried the usual things: WP debug ...
- 31
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325
views
Apache strace getsockname call is slow
While load testing I am getting almost 100% CPU usage by Apache processes. To find out the root cause I attached Apache process with strace and found slow calls.
11840 0.000063 accept4(3, {...
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1k
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DNS lookups eventually become consistently slow in long lived ruby process
I have a Ruby application running on an Ubuntu server, and this application frequently has to make HTTP requests to other services. Some of those services are on an internal domain, some are ...
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Can strace show me the filename/path for read/write syscalls
If, on Linux, I strace a process, then the reads and writes are shown with the file descriptor handle number. If I look in /proc/$PID/fd I can see the symlinks to the files that correspond to the fd ...
- 31.9k
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440
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nscd works when strace is attaching to the process
I have a server where I am running nslcd to query an AD server, and use it for authorization, and this is working as expected. Now, I introduced nscd to reduce the load on the AD servers. The results ...
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2k
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MySQL reading /etc/hosts.allow and /etc/hosts.deny
The error reporting of one of my services reported problems to connect to my MySQL server. This problems were not consistent, it just happened a few times to different servers.
I started debugging ...
- 1,170
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How do audit changes to dir via symlink?
Use of the auditd system to watch a directory via a symlink hardly triggers any logs. Here is the situation:
# pwd
/home/root/serverfault
# ls -l
total 4
drwxr-xr-x 2 root root 4096 Sep 1 15:12 ...
- 778
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0
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1k
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Apache Timeout / Deadlock When MaxClients Reached
I'm running Apache 2.2, preform MPM, on Debian Squeeze with mod_php (PHP 5.3), listening on several ports (with memcached running on the same machine). Over the past 6 weeks or so, I've been ...
- 1,157
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86
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Intentionally stop a process from responding
Is there any way to intentionally prevent a process from responding - ie. not close or kill it, but stop it dead in it's track, so it immediately stops processing anything?
I've often found myself ...
- 183
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4k
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strace not showing anything for thread at 100% 'system' CPU
I'm having difficulty with my Python app going to 100% 'system' CPU time across multiple threads for up to 10+ seconds. My (limited) understanding is that 'system' CPU time is time spent in the kernel....
- 121
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1k
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Linux high iowait without block device activity
I'm having a hard time figure out the reason cause high iowait on my server.
top:
%Cpu(s): : 30.0 us, 5.4 sy, 0.0 ni, 53.9 id, 10.1 wa, 0.0 hi, 0.7 si, 0.0 st
iostat:
Device: rrqm/s ...
- 143
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7k
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tail -f not following log file in Docker container
I am seeing some strange behavior running the tail -f command inside a Docker container in CoreOS.
There are a number of variables I can think of that may be contributing to the problem but I am not ...
- 790
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956
views
strange strace output of httpd process of apache running django with mod_wsgi
I have about 12 httpd processes running for an RHEL aws box that no one is hitting in the browser (shared team dev box). These processes together are consuming over 1.8 GB on the dev box, and I have ...
- 189
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890
views
SystemTap - filter own syscalls (system-wide trace)
I want to write simple strace-like script using SystemTap.
Main goal is to catch only some system calls (like open, close, read, write etc.) for all processes in system. (Can't do that with strace ...
- 123
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750
views
Apache stops communicating with memcache after creating too many vhosts
I've noticed a very peculiar problem with Apache. I have a very high number of virtual hosts set up - it's around 501.
Problems started occuring after vhost number 493. First 493 vhosts work as ...
- 5,267
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670
views
TCP packet which is absent in strace log
Can somebody give me ideas about following situation (Linux 2.6.18-348.4.1.el5 ):
At some point tcpdump shows [FIN, ACK] packet sent from server port to local client
strace log shows no socket ...
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6
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1
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2k
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strace shows long time reading from mysql socket - mysql takes long time to execute query?
My Apache server takes long time to process request. I attached strace to it and can see the two following delays:
1) Very critical (143 seconds to process)
1335 0.000037 write(16, "\235\0\0\0\...
- 767
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420
views
upstart - supervisord fork count > 2 (can;t get supervisord to start on boot)
i'm trying to use upstart so that supervisord starts automatically at boot.
my supervisord is in a virtual environment.
I've configured it to run in foreground mode with -n param and it works if ...
- 215
2
votes
2
answers
3k
views
process works under strace but not normally
I have a process - a perl script - that does:
while true
check a POP account on a server on the lan
process any email found
write logs - messages found, actions taken, errors
sleep ...
- 797
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95
views
How to watch a file, who accesses or uses [duplicate]
I am looking forward a way to watch a file to get following information
Which process does open, read, write it?
When?
Result. (e.g. can they write on it, or can they read it, etc.)
Strace helps us ...
- 109
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1
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294
views
Tracing system calls is slow on a KVM VPS?
I run a website on a KVM VPS and I noticed that processes appear to run extremely slowly when being traced. For example, I ran ls on my home directory, which contains 72 files and directories.
With ...
- 347
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1k
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Apache web server maxing out due to processes stuck at D status
I have a Apache 2.2.3 web server running on a 8 core VM with 8G Ram.
During a load test, the web server stopped responding and load average went up to 1000.
When I run Top command, I see a large ...
- 121
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2
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784
views
MySQL hangs if connection comes from outside the LAN
I have a MySQL Server operating just fine if I access him from his local LAN (192.168.100.0/24). If I try to access hin from another LAN (192.168.113.0/24 in this case) it hangs for a really long time ...
- 388
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118
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MySQL sandbox strace option
Latest MySQL Sandbox version uses environment variable SBDEBUG to start mysql instances in debug mode, but i can't pass mysql --debug option.
export SBDEBUG=d:t:O,/tmp/client.trace
cd ~/sandboxes/...
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155
views
Debugging high CPU load when adding new domain inside server's control panel
When adding a new domain inside my server's control panel it takes much longer than usual since some time.
CPU shows 100% usage on one core and strace reports something like this:
poll([{fd=7, ...
- 568
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3
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3k
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Troubleshooting SUDO Slowness with STRACE
I'm having trouble with sudo on some systems. It is taking anywhere from 15-30 seconds to complete a sudo command or to even login to the system.
I ran an strace and can see where the delay is ...
- 369
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727
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mongodb mystery crashes with sigkill under strace
I have a mongodb instance that seems to crash roughly once a day. I don't see any useful information in the mongo log file. All is well and then the process is just crashed with no additional ...
- 283
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742
views
strace vs. log4cxx performance hit?
I need to debug some issue on a production server, and I'm trying to decide whether to use strace or the log4cxx logging library; one crucial characteristic I need to know before, is which of the two ...
- 357
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856
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mysql client slow login strace
I am experiencing an issue with slow connections/logins to a loaded mysql server, even when connecting via the unix socket file (CentOS 6.3). Queries are completing very quickly -- (0.00 sec) in this ...
- 815
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6
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124k
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Find out what high CPU usage apache process is actually doing?
Currently having a few issues with our server where, intermittently, we seem to get apache processes which just run and run, taking up 100% CPU.
When running top, we see the following:
PID USER ...
- 551
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3
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1k
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Mysql killing the CPU with gettimeofday
I have a problem with mysql killing the CPU on a Debian Squeeze 64.
This is a development machine on a VPS so I stopped all the other services, including apache2.
The mysql version is 5.1.49. This is ...
- 121