markdown 我的linux片段为RHCSA

Posted 2021-05-06

# Some Linux snippets for  preparation to RHCSA.
Only necessary for rhcsa topics
Some links:

 - https://www.certdepot.net/rhel7-get-started-systemd/

## Working with text


### AWK

Get users with uid > 1000

	awk -F'[/:]' '{if ($3 >= 1000 && $3 != 65534) print $1}' /etc/passwd

### Grep
Links:

 - http://najomi.org/_nix/grep

Config without comments and blank lines

    cat /etc/httpd/conf/httpd.conf  | grep -v -E "(^\s*#|\s*^;|^$)" 

Check upstreams in nginx conf

    for i in $(grep -oE "(10.193.16.[0-9]{2}:[0-9]*)" * |cut -d: -f2,3 | sort -n | sort -u) ; do curl -s -o /dev/null -w "$i-%{http_code}\n" $i  | grep 000;done


Top-50 nginx requests

	zgrep -E '\[06\/Aug\/2018:0[9,12]:\w+:\w+\s+.*\]' access.gz |  awk '{print $7}' | sort -n | uniq -c | sort -nr | head -n 50

Find files with sometext or SOMETEXT in /etc/httpd

    grep -rli sometext /etc/httpd/
    
Grep current ip addresses. Syntax:
	**ip a | grep 'inet '** * 		only ipv4 addreses (ipv6 strings contais 'intet6')
	 **grep -Po**  'P' using perl regexp, 'o' only match
	 **'(\d+\.){3}\d+'** 		'(\d+\.){3}\d+' Three groups of several numbers + dot + another 4th group of digits.
	 **(?=\/)** 		match '/' after ip address, but not including it

     ip a | grep 'inet ' | grep -v 127.0.0 | grep -Po '(\d+\.){3}\d+(?=\/)'

Find files in /etc folder that contains any of host's ip address. Syntax: xargs work as for loop, ip is a variable, something like:  
for ip in addresses:  
grep  -rli ip /etc/


    ip a | grep 'inet ' | grep -v 127.0.0 | grep -Po '(\d+\.){3}\d+(?=\/)' | xargs -I ip grep  -rli ip /etc/

200 OK per second

    tail -f /var/log/nginx/*.log | grep —color=always  '"200"' |  perl -e 'while (<>) {$l++;if (time > $e) {$e=time;print "$l\n";$l=0}}'


### Touch
#### Modify mdata to timestamp
	find . | xargs -o  -I file touch -t 1812131145.23  file
	touch -d "2 hours ago" filename




### Sed
Links:

 - http://najomi.org/_nix/sed
 - https://www.opennet.ru/docs/RUS/bash_scripting_guide/a14586.html


Print 4th line. 
Syntax: N = Line number  !d = Do not delete.

    sed '4!d' httpd.conf
    
Syntax: -n = Nothing will print unless an explicit request to print is found.  N = Line number  p = print

    sed -n '3p'  httpd.conf

Print 1-10 lines

    sed '1,10!d' httpd.conf
    sed -n '1,10p' httpd.conf
Replace foo on too. Syntax: s/..../..../ replacement (subtitute). "g" - global, with g sed will replace all matches in string, without g ony first match in every strings.

    sed -i 's/foo/too/g
 Sed with perl regexp. Syntax: -E or -r for enabling regexp.  This example replace "userd" or "usersff" or something else to "users".

     sed -i -E 's/user\w+/users/g' httpd.com
     
  Delete first string

      sed  '1d' httpd.com 
      
  Add allow after
 
 	sed '/allow 8.8.8.8;/a allow 1.1.1.1;' -i *
## File permissions

### Chmod
![Chmod cheats](https://raw.githubusercontent.com/borgkun/RHCSA/master/rhcsa.png)

### ACL
Users lisa and mike have group office.

    useradd lisa -g office
    useradd mike -g office 

Creating directory "testacl" with no permissions for group "office" and users mike, lisa. Only root user has permission to this directory.

    mkdir test
    chown root test
    chmod 700 test
Now give access for user lisa without changing chmod.  

    setfacl -mR d:u:lisa:rwx -R test/

Syntax: 
 - *-m* modify
 - *d* (defaults)  means that all files that would create in this directory would have this acl
 - *u* and *rwx* as in chmod.
 - *R*  recursive

Now only root and lisa has full access to this folder.
     
Show acl

    getfacl test/

### Extended attributes
Add atribute

    chattr +i prog.sh
Show attributes

    lsattr prog.sh

Most usefull attributes
![enter image description here](https://raw.githubusercontent.com/borgkun/RHCSA/master/attributes.png)


## Users

### Ldap
There are two way with nslcd or with sssd. nslcd is deprecated.
For example LDAP server address is ipa.loc.

 1. You need to make sure that ipa.loc can be resoved
 2.  yum install -y openldap-clients nss-pam-ldapd (nss for nslcd)
 3. 

    authconfig --enableldap --enableldapauth \
    --ldapserver="ipa.loc" \
    --ldapbasedn="dc=loc" --enablemkhomedir --update

 (--enablemkhomedir - optional, --enableforcelegacy - optional for nslcd)
 4. `scp ipa.loc:/etc/ipa/ca.crt cert.pem` (FreeIPA)  or `scp [e-mail]:/etc/openldap/certs/cert.pem /etc/openldap/cacerts/cert.pem`(OpenLDAP)  and `authconfig --enableldaptls --update`
> ("If you installed IPA with the domain example.com then your basedn is
> `dc=example,dc=com`") https://www.freeipa.org/page/HowTo/LDAP
 5. Check `systemctl status sssd`
 6. Check `ldapsearch -x uid=admin` or `id admin`

### Local
Create user "chermander" with uid 123 and gid 123

     groupadd -g 123 chermander
     useradd -u 123 -g 123 chermander
Change group to wheel

    usermod -g wheel chermander
    or  
    usermod -g 10 chermander

Add chermander to nobody group

    usermod -G nobody chermander
Get info about expirity

    chage -l chermander
Change date expiration to 1 month. 

    chage -E  $(date -d "+1month" +"%Y-%m-%d") chermander
Delete additional groups

    usermod -G "" chermander

## Files
Create 100 Files with size 2MB

    for i in {1..100}; do dd if=/dev/zero of=$i bs=2M count=1; done
Move this files to test dir

    ls | grep -Po '\d+' | xargs -I file mv file test/
  Create tar.bzip archive with this files

      cd test ; tar -cjf ../files.tar.bzip *

  List files in archive
  

      tar -tvf files.tar.bzip
Extract files

    tar -xvf files.tar.bzip

## Network
There are several methods for network configuration
 - nmtui
 - nmcli
 - GUI nm (nm-connection-editor)
 - /etc/sysconfig/network-scripts/

Change hostname

    hostnamect set-hostname host.loc


## Managing process

### shell jobs
Runing job in background

    dd if=/dev/zero of=/dev/null &
Show jobs

    jobs
Stops the job temporarily so that it can be managed. For instance, it can be moved to the background.

    Ctrl+Z
Send the End Of File (EOF) character to the current job to indicate that it should stop waiting for further input.

    Ctrl+D

Can be used to cancel the current interactive job

    Ctrl+C
Continues the job that has just been frozen using Ctrl+Z in the background.

    bg
Brings the last job that was moved to background execution back to the foreground.

    fg
Show process

    ps aux
    ps ef 
    ps fax

Rename git branch

	git branch -m old_branch new_branch         # Rename branch locally    
	git push origin :old_branch                 # Delete the old branch    
	git push --set-upstream origin new_branch # Push the new branch, set local branch to track the new remote
	
### Tcpdump
timeout 60 tcpdump -i ens160 -n port not 22 -w /tmp/pcap
tcpdump -nr pcap | awk '{print }' | grep -oE '[0-9]{1,}.[0-9]{1,}.[0-9]{1,}.[0-9]{1,}' | sort | uniq -c | sort -n


### Disk
Sata hotplug

	echo - - - > /sys/class/scsi_host/host2/scan
	ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done

	echo 1>/sys/class/block/sdd/device/rescan

### TOP memory usage

	ps -e -o pid,user,cpu,size,rss,cmd --sort -size,-rss | head

### Find deleted files
	find /proc/*/fd -ls | grep  '(deleted)

### LVM

#### Resize

    pvcreate /dev/sdd
    vgextend vgdb /dev/sdd
    lvextend -l +100%FREE  /dev/mapper/vgmysql-lvmysql
    xfs_growfs /dev/mapper/vgmysql-lvmysql
    pvresize /dev/sda2
    lvresize -l +100%FREE /dev/VolGroup00/LogVol00%  


#### Display


	sudo lvdisplay|awk  '/LV Name/{n=$3} /Block device/{d=$3; sub(".*:","dm-",d); print d,n;}'
	dm-0 /dev/SysVolGroup/LogVolRoot
	dm-1 /dev/SysVolGroup/xen
	dm-2 /dev/SysVolGroup/db1-2
	dm-3 /dev/SysVolGroup/db1-2swap
	dm-4 /dev/SysVolGroup/python1
	dm-5 /dev/SysVolGroup/python1swap
	dm-6 /dev/SysVolGroup/db1-2snap


### Nginx

#### pfx to key and cer for nginx

	openssl pkcs12 -in cert.pfx -nocerts -nodes -out cert.ru.key
	openssl pkcs12 -in cert.pfx -clcerts -nokeys -out cert.ru.cer
	
### Grafana
#### reset password in sqllite

	update user set password = 	'59acf18b94d7eb0694c61e60ce44c110c7a683ac6a8f09580d626f90f4a242000746579358d77dd9e570e83fa24faa88a	8a6', salt = 'F3FAxVm33R' where login = 'admin'