grep is a program for finding mathing patterns, it will look for context of a files or stdin.
grep error /var/log/server.log will print all the errors in a file.
find . -name *.txt | grep temp will print all the .txt file with temp in it.
Flags:
grep -i make search case-insensitive.
grep -r make search recursive through a directory structure.
grep -v print all the instances where is no match.
grep -w find only word pattern matches.
Regex:
^ match at the begginng of the line.
$ match at the end of the line.
\ escape special meaning of the character like \$ will match dollar sign and not an end of the line.
[] match any of the characters enclosed in the brackets [abcde] or [a-e] for range.
[^] match any except of characters in the brackets [^abcde] or [^a-e].
. match any single character.
* match zero or more of preceding character or expression.
\{x,y\} match x to y occurences of the preceding.
\{x\} match exactly x occurences of the preceding.
\{x,} match x or more occurences of the preceding.
grep '[Ll]inux' files search for Linux or linux.
umask is a tool to create a masking for file permissions. It's working the following way:
File permissions is 777
And mask is set to 555
New file will have 222 permissions
umask is usefull if you need to create a lot of files with same permissions.
umask is not persistent. To make umask persistent go to /etc/profile and /etc/bashrc.
rsyslogd is a logging service, that supports local and remote logging.
/etc/rsyslog.conf show what and where rsyslogd saves.
/var/log/ is a standard directory for storring logs.
logrotate tool for log rotation based on size, length or time.
/etc/logrotate.conf logrotate configuration file.
journalctl systemd keeps logs in a binary format as well, journalctl helps querying the logs in a faster way.
virt-manager - GUI tool to control VMs.
virt-install - tool to install a new VM from cli.
virsh - tool to edit virtual machines.
Rather than addressing disks lvm provides a way to of addressing a pool of space to manage groups.
<pvcreate> /dev/xvda1 /dev/xvda2 create physical volume command.
<vgcreate> MyVG /dev/xvda1 /dev/xvda2 create virtual group out of physical volume.
<lvcreate> -L 50m MyVG create a logical volume that can be mounted.
NFS is part of the nfs-utils package.
getfacl - get ACL permissions setfacl - set ACL permissions
setfacl -m u:tonnystark:rwx file
setfacl -m g:avengers:rwx file
Quick Set ACL
getfacl file1 | setfacl --setfile=- file2
Important files for network management: /sys/class/net - connected network devices /etc/sysconfig/network-scripts - network configuration files
nmcli is RedHat tool to manage network configuration bash-completion is recommended for this package.
Show available network devices:
nmcli dev show
Show available connections:
nmcli con show
Add connection example:
nmcli con add con-name newconnection autoconnect off type ethernet ifname eth0 ipv4.address 10.0.0.100
New connection should appear at /etc/sysconfig/network-scripts/ifcfg-newconnection.
id command will show user id.
getent command to show user related information such as id, group etc...
usermod tool to modify users.
Important files and folders:
/etc/passwd- file that contains user information./etc/shadow- contains encrypted user information./etc/group- defines groups to which user belongs./etc/skel/- folder that contains important default user files such as .bash-rc ./etc/login.defs- file that defines how system will create user, which uid can be choosen, which folder to create./etc/default/useradd- define where the skel is, which terminal to use for new user.
chage tool that lets you define password how frequently password should be changed, when user will expire/inactive.
chage -l show the account aging information.
chage -M set the maximum value of days during which password is valid.
chage -I set the number of days of inactivity after a password expiration before the account is locked.
chage -E set the account expiration date.
This parameters could be set system-wide in /etc/login.defs and /etc/default/useradd.
usermod -g change user primary group.
usermod -G change user suplimentary group.
getent group check users group.
groupadd create new group.
groupmode modify group same as usermod, changing group id will make all files owned by this group without owner.
Netfilter is a kernel module that enables user manipulations over network packets suck as packet filtering, network address translation and port translation.
iptables old way of manipulation netfilter module.
firewalld is a service that implements firewall by manipulation netfilter module.
firewall-cmd is a cli tool to make changes to local firewall.