Tag: linux

To change shell for a user, run

chsh --shell PATH_TO_SHELL USERNAME

Example

chsh --shell /bin/bash okadmin

I will add a user, if no shell specified, it use sh as shell.

root@lab:~# useradd okadmin
root@lab:~# su - okadmin
No directory, logging in with HOME=/
$ echo $SHELL
/bin/sh
$ exit
root@lab:~# chsh --shell /bin/bash okadmin
root@lab:~# su - okadmin
No directory, logging in with HOME=/
okadmin@lab:/$ echo $SHELL
/bin/bash
okadmin@lab:/$ logout
root@lab:~# 

You can find what shell you are using now with command

echo $SHELL

To identify if you are using 32 bit or 64 bit Linux OS, run command arch.

boby@sok-01:~$ arch
x86_64
boby@sok-01:~$

You can also use uname command

boby@sok-01:~$ uname -i
x86_64
boby@sok-01:~$ 

Another way is to use hostnamectl command and look for “Architecture”.

boby@sok-01:~$ hostnamectl
   Static hostname: sok-01
         Icon name: computer-desktop
           Chassis: desktop
        Machine ID: 70486772aac1410c9a8031851ab60a0d
           Boot ID: 46ff31881cca4e7090edb35f2af89a4a
  Operating System: Ubuntu 18.04.2 LTS
            Kernel: Linux 4.15.0-55-generic
      Architecture: x86-64
boby@sok-01:~$ 

aplay

sudo alsa force-reload 

vi /etc/modprobe.d/alsa-base.conf

Show Sound Devices

boby@fwhlin:~$ cat /proc/asound/cards
 0 [Intel          ]: HDA-Intel - HDA Intel
                      HDA Intel at 0xfb9f8000 irq 75
 1 [HDMI           ]: HDA-Intel - HDA ATI HDMI
                      HDA ATI HDMI at 0xfbcfc000 irq 76
boby@fwhlin:~$

boby@boby-pc ~ $ cat /proc/asound/card0/codec* | grep Codec
Codec: Realtek ALC892
boby@boby-pc ~ $ 

boby@boby-pc ~ $ cat /proc/asound/card0/pcm0c/info
card: 0
device: 0
subdevice: 0
stream: CAPTURE
id: ALC892 Analog
name: ALC892 Analog
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 1
boby@boby-pc ~ $ 

General

• arch
• chsh – Change Linux user shell
• apropos
• whois
• uname
• chown
• at
• lynx
• setfacl
• tr
• gifsicle
• chattr
• chmod

System

strace
lsof
lspci

Networking

nmtui – configure networking

Disk/Storage

blkid – show UUID for disks.
vgcreate

Load

• vmstat
• atop
• top

# strace -p 17723
-bash: strace: command not found
# 

This is because strace not installed on the server. Install it with yum

# yum install strace
Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Reading repository metadata in from local files
Parsing package install arguments
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Downloading header for strace to pack into transaction set.
strace-4.5.16-1.el5.1.i38 100% |=========================|  15 kB    00:00
---> Package strace.i386 0:4.5.16-1.el5.1 set to be updated
--> Running transaction check

Dependencies Resolved

=============================================================================
 Package                 Arch       Version          Repository        Size
=============================================================================
Installing:
 strace                  i386       4.5.16-1.el5.1   base              163 k

Transaction Summary
=============================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total download size: 163 k
Is this ok [y/N]: y
Downloading Packages:
(1/1): strace-4.5.16-1.el 100% |=========================| 163 kB    00:00
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing: strace                       ######################### [1/1]

Installed: strace.i386 0:4.5.16-1.el5.1
Complete!
#

strace command is used to trace system calls. This is useful to see what a process is doing.

To see what a process doing, run

strace -p PID_HERE

To run a command and strace

strace cat 1.txt

Debug apache start up

strace -Ff -o output.txt -e open /etc/init.d/httpd restart
cat output.txt | grep '= -1'

When installing a software from source, i get error

configure: error: can't find pcap.h
  You're not going to get very far without libpcap.

To fix this on CentOS 7 server, run

yum -y install libpcap libpcap-devel