Discuss April 2021

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enough free pages but high number of major page faults and page reclaims
by yf chu 17 Apr '21

17 Apr '21

We find that for some servers io disk read is very high. We also notice that there are many major page faults on those servers. But we checked the /proc/zoneinfo, there are enough free pages. Here is the content of /proc/zoneinfo: pages free 3913507 min 11333 low 14166 high 16999 scanned 0 spanned 16777216 present 16777216 managed 16507043 nr_free_pages 3913507 We also use "perf" to monitor the event of "mm_filemap_delete_from_page_cache". Here is the result of perf: 7fff81189dd0 __delete_from_page_cache ([kernel.kallsyms]) 7fff8119b771 __remove_mapping ([kernel.kallsyms]) 7fff8119c8e8 shrink_page_list ([kernel.kallsyms]) 7fff8119d45a shrink_inactive_list ([kernel.kallsyms]) 7fff8119df55 shrink_lruvec ([kernel.kallsyms]) 7fff8119e376 shrink_zone ([kernel.kallsyms]) 7fff8119e880 do_try_to_free_pages ([kernel.kallsyms]) 7fff8119ed6c try_to_free_pages ([kernel.kallsyms]) 7fff816ac515 __alloc_pages_slowpath ([kernel.kallsyms]) 7fff811932d5 __alloc_pages_nodemask ([kernel.kallsyms]) 7fff811d7a68 alloc_pages_current ([kernel.kallsyms]) 7fff811e27f5 new_slab ([kernel.kallsyms]) 7fff811e40fc ___slab_alloc ([kernel.kallsyms]) 7fff816adaf1 __slab_alloc ([kernel.kallsyms]) 7fff811e609b kmem_cache_alloc ([kernel.kallsyms]) 7fff812778ed proc_alloc_inode ([kernel.kallsyms]) 7fff812234d0 alloc_inode ([kernel.kallsyms]) 7fff81225771 new_inode_pseudo ([kernel.kallsyms]) 7fff812257d9 new_inode ([kernel.kallsyms]) 7fff8127bc1e proc_pid_make_inode ([kernel.kallsyms]) 7fff812800e5 proc_fd_instantiate ([kernel.kallsyms]) 7fff8127c54c proc_fill_cache ([kernel.kallsyms]) 7fff812802dd proc_readfd_common ([kernel.kallsyms]) 7fff812803f5 proc_readfd ([kernel.kallsyms]) 7fff8121c246 vfs_readdir ([kernel.kallsyms]) 7fff8121c665 sys_getdents ([kernel.kallsyms]) 7fff816c2715 system_call_fastpath ([kernel.kallsyms]) bab95 __getdents64 (/usr/lib64/libc-2.17.so) It seems that os is carrying on page reclaim. But I don't know since there are enough free pages, why could page reclaim ocurr?

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Proxmox Backup Server equivalent for the RHEL/CentOS world ?
by Nicolas Kovacs 17 Apr '21

17 Apr '21

Hi, I've just spent a couple weeks experimenting extensively with Proxmox VE (Virtual Environment) and Proxmox PBS (Backup Server) on a couple of sandbox servers. I must say I'm impressed, especially of the elegance and simplicity of the backup solution. Running virtual machines can be backed up efficiently, combining deduplication and incremental backups. A bit like Rsnapshot, only for whole VM images. Both PVE and PBS are based on Debian, and now I wonder if RHEL-based systems have something similar to offer. Any suggestions ? Niki -- Microlinux - Solutions informatiques durables 7, place de l'église - 30730 Montpezat Site : https://www.microlinux.fr Blog : https://blog.microlinux.fr Mail : info(a)microlinux.fr Tél. : 04 66 63 10 32 Mob. : 06 51 80 12 12

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CentOS-announce Digest, Vol 193, Issue 2
by centos-announce-request＠centos.org 15 Apr '21

15 Apr '21

Send CentOS-announce mailing list submissions to centos-announce(a)centos.org To subscribe or unsubscribe via the World Wide Web, visit https://lists.centos.org/mailman/listinfo/centos-announce or, via email, send a message with subject or body 'help' to centos-announce-request(a)centos.org You can reach the person managing the list at centos-announce-owner(a)centos.org When replying, please edit your Subject line so it is more specific than "Re: Contents of CentOS-announce digest..." Today's Topics: 1. CESA-2021:0742 Important CentOS 7 screen Security Update (Johnny Hughes) ---------------------------------------------------------------------- Message: 1 Date: Wed, 14 Apr 2021 13:29:09 +0000 From: Johnny Hughes <johnny(a)centos.org> To: centos-announce(a)centos.org Subject: [CentOS-announce] CESA-2021:0742 Important CentOS 7 screen Security Update Message-ID: <20210414132909.GA20207(a)bstore1.rdu2.centos.org> Content-Type: text/plain; charset=us-ascii CentOS Errata and Security Advisory 2021:0742 Important Upstream details at : https://access.redhat.com/errata/RHSA-2021:0742 The following updated files have been uploaded and are currently syncing to the mirrors: ( sha256sum Filename ) x86_64: 30b844415ba647e65a9810574f3ded5e1fc1edd02e28f73cc44ee2c35e97baea screen-4.1.0-0.27.20120314git3c2946.el7_9.x86_64.rpm Source: 8110b0f5f7bc0070b8cd656a7965d0f7d2f7c69102bbd80dbfc966ea718f96d8 screen-4.1.0-0.27.20120314git3c2946.el7_9.src.rpm -- Johnny Hughes CentOS Project { http://www.centos.org/ } irc: hughesjr, #centos(a)irc.freenode.net Twitter: @JohnnyCentOS ------------------------------ Subject: Digest Footer _______________________________________________ CentOS-announce mailing list CentOS-announce(a)centos.org https://lists.centos.org/mailman/listinfo/centos-announce ------------------------------ End of CentOS-announce Digest, Vol 193, Issue 2 ***********************************************

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rsync over ssh stalls after completing the job
by Frank Cox 15 Apr '21

15 Apr '21

Here's a weird one. I have two Centos 8 machines that use rsync-over-ssh to back up files between each other. (Each machine acts as a backup machine for the other one.) There's are nightly cronjobs that do the backing up, the commands look like this: rsync -av --delete /home/mydirectory jeff:/home/mydirectorybackup That command works fine when it's run through the cronjob. When I try to run a rsync command between mutt and jeff from the commandline, that's where the problem starts. It worked a few days ago but now when I log into jeff and do a rsync to or from mutt it works fine. When I log into mutt and do a rsync to or from jeff it works and does the job, but then it seems to stall afterward and I have to hit ctrl-c to get my cursor back. Here's a test run so you can see what happens. [me@mutt temp]$ rsync -avv ../temp/ jeff:temp opening connection using: ssh jeff rsync --server -vvlogDtpre.iLsfxC . temp (7 args) sending incremental file list delta-transmission enabled bookmarks.html is uptodate ./ abc total: matches=0 hash_hits=0 false_alarms=0 data=26321 ^Crsync error: received SIGINT, SIGTERM, or SIGHUP (code 20) at rsync.c(644) [sender=3.1.3] A file named bookmarks.html existed in both directories so it wasn't changed, and a new file abc was copied to the backup directory. Then my ctrl-c stopped the job and brought the cursor back after it stalled. scp works fine to copy files either way when logged into either machine and, again, my backup-this-to-that cronjobs that run rsync seem to be working fine as well. I just discovered this last night when I went to rsync some files manually between these machines. The last time I did that was at least a few days ago and it worked fine then. -- MELVILLE THEATRE ~ Real D 3D Digital Cinema ~ www.melvilletheatre.com

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NAME:WRECK
by mark 14 Apr '21

14 Apr '21

I'm reading a story linked to from slashdot, and I see FreeBSD is vulnerable. Has anyone looked at CentOS? mark

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Missing /etc/ld.so.conf.d/kernel-3.10.0-1127.19.1.el7.x86_64.conf
by Kenneth Porter 14 Apr '21

14 Apr '21

I'm yum updating some CentOS 7 systems today and got this error. Two systems (so far) seem to have rebooted fine. Should I worry? error: file /etc/ld.so.conf.d/kernel-3.10.0-1127.19.1.el7.x86_64.conf: No such file or directory

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Re: [CentOS] Proxmox Backup Server equivalent for the RHEL/CentOS world ?
by Blaž Bogataj 14 Apr '21

14 Apr '21

Hello As I said a couple of weeks ago in response to Niki I have been using ProxMox almost from the beginning ;). No "enterprise" version. And backup is one of the reasons for that. NFS on NAS as a backup target is really nice, even one time quicker than backup to local storage (NAS with 10gb FC). Also fiddling with RHV. But there is no "free" backup solution. I am trying with Bacchus but no way to schedule backup. Single backup OK, schedule backup no go. So now use vProtect, for 5 years not a lot of $. But I hope to find some instructions on how to build Prox and use it as software defined storage. I must learn how to build this, especially about a separated management network, without I think I can't build this to get HA. And them migrate from RHV. All the best Blaz

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What to do when a selinux policy doesn't work?
by hw 14 Apr '21

14 Apr '21

Hi, I'm getting log file entries about ejabberd not being able to remove files that were uploaded by client through the file upload facility of XMPP. With the help of audit2allow, I have already created and installed some selinux modules to solve such issues, and still files can't be expired. So I used grep '/srv/data/ejabberd' /var/log/audit/audit.log | audit2allow -w to find out what might cause this, and the answer is: type=AVC msg=audit(1606302910.314:2905): avc: denied { open } for pid=18687 comm="8_dirty_io_sche" path="/srv/data/ejabberd/[...]" dev="md100" ino=166 scontext=system_u:system_r:ejabberd_t:s0 tcontext=system_u:object_r:var_t:s0 tclass=file permissive=1 Was caused by: Unknown - would be allowed by active policy Possible mismatch between this policy and the one under which the audit message was generated. Possible mismatch between current in-memory boolean settings vs. permanent ones. I have reloaded the policies with 'semodule -R', and that didn't change anything. The files in question seem to have the correct attributes like: ls -laZ /srv/data/ejabberd/[...] -rw-r--r--. 1 ejabberd ejabberd system_u:object_r:var_t:s0 1384362 Nov 25 12:15 /srv/data/ejabberd/[...] Ejabberd is supposed to expire files when they are older than desired, and selinux prevents it. How can I solve this problem other than by disabling selinux or by deleting the files manually?

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How to find out what's eating the bandwidth
by Frank Cox 14 Apr '21

14 Apr '21

Is there a program that will tell me what's eating the bandwidth on a lan? I'm thinking of something that would tell me that a.b.c.d is using so many mbps and a.b.c.e is using this many and so on. Or can just-another-computer-on-the-network actually see that sort of information? I don't know enough about the low level nuts and bolts of networking to know if it has that kind of access. I'm really just interested in volume of traffic per attached device rather than specific origin/destination information if that's easier to obtain. This way if something is eating the network I can find out what it is without having to start unplugging cables and so on to find out when it stops. -- MELVILLE THEATRE ~ Real D 3D Digital Cinema ~ www.melvilletheatre.com

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How to organize your VMs
by Nicolas Kovacs 13 Apr '21

13 Apr '21

Hi, Up until now my main production server has been a "bare metal" installation of CentOS 7.9 hosting a variety of stuff. * DNS server with BIND for eight domains * IMAP mail server with Postfix and Dovecot for these domains, with about two dozen mail accounts * Webmail with Roundcube for all the mail accounts * Various WordPress-based websites and blogs * Several instances of the management software Dolibarr * The learning platform GEPI for our local school * One instance of OwnCloud for half a dozen users The hardware has no problems to deal with all that performance-wise. But managing all this in one big bulk has become a bit of a problem, since the LAMP-based PHP applications (WordPress, Dolibarr, GEPI, OwnCloud) increasingly cultivate their idiosyncrasies, so this feels more and more like herding cats. My main goal in migrating all this stuff preogressively to a series of neat VMs hosted on a KVM hypervisor is clarity and ease of maintenance. Now I wonder what could be a smart subdivision of all these VMs. After a bit of brainstorming, here's what I can come up with. 1. It would make sense to regroup all the applications, e. g. one VM for all the Dolibarr hostings, and then a different VM for WordPress, and a third VM for OwnCloud. 2. It's tempting to have a lot of small VMs for clarity's sake. On the other hand, it's maybe better to have one single VM for all the mail stuff. 3. Should I put all the Roundcube instances in a separate VM? Or does that go with the Postfix/Dovecot mail VM? 4. DNS is a bit of a special case, a bit of a catch 22. I would be tempted to setup an extra (bare-metal) machine for just handling this. Since BIND provides the DNS information about the hypervisor and the backup server themselves this becomes a bit of a chicken-and-egg situation. 5. Even if it's tempting to multiply VMs, let's not forget that I have to keep an eye on hardware resources, not to forget I have to pay for every extra IPv4 address. I'd be curious to have your input, since I'm fairly new to this sort of approach. Cheers, Niki -- Microlinux - Solutions informatiques durables 7, place de l'église - 30730 Montpezat Site : https://www.microlinux.fr Blog : https://blog.microlinux.fr Mail : info(a)microlinux.fr Tél. : 04 66 63 10 32 Mob. : 06 51 80 12 12

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Discuss April 2021