mkdocs-benoit.jp.net/docs/Howtos/HowtoSysadmin.md
2021-02-20 15:06:15 +09:00

235 lines
7.2 KiB
Markdown
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

Get Github or Gitlab user key:
```console
$ curl https://github.com/<username>.keys
$ curl https://gitlab.com/<username>.keys
```
Enter a namespace, for example LXD (which is in a NS by Snap).
```console
$ nsenter -t $(cat /var/snap/lxd/common/lxd.pid) -m
```
SSH into a machine without checking host key. Useful when servers are in a rescue mode.
```console
$ ssh -o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no" -o "GlobalKnownHostsFile=/dev/null"
```
Certbot manual example.
```console
# certbot certonly --non-interactive --webroot --webroot-path /var/www/html/ -d foo.bar -d www.foo.bar
```
GPG-agent list SSH key and remove.
```
gpg-connect-agent
KEYINFO --ssh-list --ssh-fpr
DELETE_KEY $HASH
```
Show md5 fingerprint of SSH key.
```console
$ ssh-keygen -l -E md5 -f .ssh/key.pub
```
Password recovery. At grub stage, press `e` to edit the kernel line and add `init=/bin/bash`. It will drop you in a shell before init system (systemd).
```console
# mount -o remount,rw /
# passwd
```
Mount partitions on an image file using losetup.
```console
# losetup -P -f --show my.img
```
List all software installed from particular component (non-free, contrib)
```console
$ dpkg-query -W -f='${Section}\t${Package}\n' | grep ^non-free
```
Manually rotate a file without logrotate, with savelog(8).
```console
$ savelog
```
What processes uses swap?
```console
$ for file in /proc/*/status ; do awk '/VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | sort -k 2 -n -r | less
```
MySQL "fast" shutdown.
```console
> set global innodb_max_dirty_pages_pct = 0;
$ mysqladmin ext -i10 | grep dirty
```
mkfs.ext4 for old systems in rescue mode (Debian Wheezy, …).
```console
# mkfs.ext4 -O ^64bit,^metadata_csum
```
Send a mail from queue.
```console
$ postcat -q ID > mail
$ < mail sendmail -f FROM TO
```
Python Simple HTTP Server (useful for Munin for example).
```console
$ cd /var/cache/munin/www
$ python -m SimpleHTTPServer 8080
```
Show custom certs (not a link) and expiration in `/etc/ssl/certs`.
```console
# find /etc/ssl/certs/ -type f -print -exec openssl x509 -text -in {} \; | grep --color=auto -e etc -e CN= -e DNS: -e After;
```
Edit Bind DNS serial (needs modifications, not generic).
```console
$ sed -ri 's/^\s*[0-9]+\s*; serial/\t\t\t 2017041010\t ; serial/' db.*
```
After Debian/Ubuntu upgrade, merge local config files according to config files shipped in packages.
```console
# for file in $(find /etc -iname '*.dpkg-dist'); do vimdiff ${file%%.dpkg-dist} $file; rm $file; done
# for file in $(find /etc -iname '*.dpkg-old'); do vimdiff ${file%%.dpkg-old} $file; rm $file; done
# for file in $(find /etc -iname '*.dpkg-new'); do vimdiff ${file%%.dpkg-new} $file; rm $file; done
# for file in $(find /etc -iname '*.ucf-dist'); do vimdiff ${file%%.ucf-dist} $file; rm $file; done
# for file in $(find /etc -iname '*.ucf-old'); do vimdiff ${file%%.ucf-old} $file; rm $file; done
# for file in $(find /etc -iname '*.ucf-new'); do vimdiff ${file%%.ucf-new} $file; rm $file; done
```
Debug php with strace and php-cgi (especially useful for wp multisites).
```console
$ HTTP_HOST=www.site.com SCRIPT_FILENAME=index.php REDIRECT_STATUS=CGI SERVER_NAME=www.site.com strace -s 65535 -o /tmp/strace php-cgi -f index.php
```
`ps` with long user fields (here 20).
```console
$ ps axo user:20,pid,pcpu,pmem,vsz,rss,tty,stat,start,time,comm
```
WTF is happening in apache (or other)? Let's strace all apache processes.
```console
# strace -p $(ps auwwwx | grep apache | tr -s '\t' ' ' | cut -d' ' -f2 | tr '\n' ' ' | sed 's/ / -p /g') 9999
```
WTF is happening? Let's tail all logs.
```console
# tail -f $(lsof | grep -F .log | tr -s '\t' ' ' | cut -d' ' -f10 | sort | uniq | tr -s '\n' ' ')
```
Search for suspects POST in apache.log (often attacks).
```console
# grep -Eo '"POST .*.php' access.log | grep -ve cron -e login -e admin -e xmlrpc -e trackback -e comment -e 404 | sort -u
```
Check for crashed MySQL table in syslog and launch a repair.
```bash
#!/bin/bash
tables=$(grep crashed /var/log/syslog | grep -Eo \'\./.*\' --color=auto | sed s#\'./## | sed s#\'## | uniq | tr -s '\n' ' ')
for tableC in $tables; do
db=${tableC%/*}
table=${tableC#*/}
mysqlcheck --auto-repair --check $db $table
done
```
Get the groups of an user and add another user into these groups.
```console
# for group in $(grep user1 /etc/group | cut -d':' -f1 | sed '/user1/d'); do adduser user2 $group; done
```
Get the last acceded URLs in Squid Access list.
```console
# tail -n100 /var/log/squid3/access.log | grep -oE 'http.*' | cut -d ' ' -f1 | sort | uniq
```
Migrate MySQL users.
```console
# #SRC Server
# mysql mysql -e "select * from user WHERE USER='user1' OR USER='user2' INTO OUTFILE '/tmp/mysql_user';"
# mysql mysql -e "select * from db WHERE USER='user1' OR USER='user2' INTO OUTFILE '/tmp/mysql_db';"
# #DST Server
# scp server:/tmp/mysql_{db,user} /tmp
# chmod 664 /tmp/mysql_{db,user}
# mysql mysql -e "LOAD DATA INFILE '/tmp/mysql_user' INTO TABLE user;"
# mysql mysql -e "LOAD DATA INFILE '/tmp/mysql_db' INTO TABLE db;"
```
Find userid of mails in mailq.
```console
$ for i in $(mailq | grep -Eo [A-F0-9]{10} | tr -s '\n' ' '); do postcat -q $i | grep userid | grep -Eo "[0-9]{4,}" >> tmp/userid; done
$ sort -n /tmp/userid | uniq
```
Kill every MySQL SELECT older than X seconds Original: https://anothersysadmin.wordpress.com/2008/10/29/kill-every-mysql-select-older-than-x-seconds/
```bash
#!/bin/bash
# From https://anothersysadmin.wordpress.com/2008/10/29/kill-every-mysql-select-older-than-x-seconds/
SEC=$1
IFS='|'
if [[ $SEC -lt 1 ]]; then
echo "Usage: $0 SECONDS"
exit 1
fi
mysqladmin proc -v|grep Query|grep -Evi "delete|update|insert|alter table" |while read dummy qid qusr qhost qdb qstat qsec qstat2 query; do
if [ $qsec -gt $SEC ]; then
echo "Killing query $qid..."
mysqladmin kill $qid
fi
done
```
List of contacts when sending a mail for technical purpose on a domain which doesn't announce their technical contacts in a whois.
```
abuse@<domain>, admin@<domain>, administrator@<domain>, contact@<domain>, info@<domain>, postmaster@<domain>, support@<domain>, webmaster@<domain>
```
itk change rights.
```console
# find /tmp/ -user www-user.old -exec chown www-user:user {} \;
# find /tmp/ -user user.old -exec chown user:user {} \;
* Détecter les fichiers non lisibles par Apache (lecture sur le groupe) : find ./ -type f ! -perm /g=r -exec ls -l {} \;
* Détecter les répertoires non lisibles par Apache (lecture/exécution sur le groupe) : find ./ -type d \( ! -perm /g=r -o ! -perm /g=x \) -exec ls -ld {} \;
* Détecter les fichiers/répertoires accessibles en écriture par Apache (écriture sur le groupe) : find ./ -perm /g=w
* Détecter les fichiers/répertoires accessibles en écriture par tous : find ./ -perm -007 -o -type f -perm -006
```
Get useradd command for migrating account.
```console
# for i in user1 user2 user3...; do echo -n 'useradd -m -s /bin/bash -u '$(grep -E "^$i" /etc/passwd | cut -d':' -f3) && echo -en ' -p' \'$(grep -E "^$i" /etc/shadow | cut -d ':' -f2)\' $i '\n'; done
Output :
useradd -m -s /bin/bash -u USERID -p 'USERPWD' username
```
Find files newert than (mtime) a precise date, and execute an action.
```bash
# find . ! -newermt '2012-09-19 11:40:00' -exec cp {} /tmp/mails \;
```