Q001:-How do you execute a UNIX command in the background?
Script &, screen |
Q002:-Explain iostat, vmstat and netstat.
Iostat :- Report CPU statistics, and input/output statistics for devices and partitions.
VMSTAT:- vmstat reports information about processes, memory, paging, block IO, traps, and CPU activity.
NETSTAT:- netstat displays a list of open sockets. |
| Q003:-Explain soft(symbolic)/hard link and difference.
A soft link is a pointer to something else in the file hierarchy. Thus it matters where on the visibly exposed hierarchy a file resides. This is why they can point to things on different filesystems, as long as they are mounted in a consistent spot.
Ex: ext2 partition mounted /mnt/a, reiserfs partition mounted /mnt/b, symlink /mnt/a/mylink -> /mnt/b/my_real_file
If b were unmounted, this link goes away. if a were mounted again as b, the association would also not work. this isn’t magic. There is time spent handling this redirection, that you don’t have with hard links. Accessing a symlink makes it need to find the symlink, realize it’s a symlink, then go to the actual file.
Hard link: different inodes representing the same physical location on the disk. Obviously can’t go outside of its partition boundaries (and be legal). Thus /file1 and /file2 are hard linked to the same physical location on the disk. There is no redirection here as there is with symlinks.
different
A hard link cannot span file systems.
A soft link can point to files anywhere on the network.
All hard links share the same inode number.
Each soft link has a unique inode number.
If you delete the source hard link file you can still access the other one. However, with a soft link, if you delete the source link, you cannot access the other one.
With a soft link, you can create a symbolic link to a file that does not exist yet. You cannot create a hard link unless the source file already exists. |
| Q004:-what is Kernel parameters?
Kernal parameters are nothing but all the parameters in
/etc/sysctl.conf here we can edit according to our requirements. |
| Q005:-How to check many CPUs have been used in your machine?
to check the how many CPUs are in the machine just type this
command #psrinfo to check the CPU spec
#psrinfo –v |
| Q006:-what is a daemon?
A process that runs in the background and performs a specified operation at predefined times or in response to certain events. |
| Q007:-I want to change the run level but the Users shall not be disturbed. how?
Init (run level)
systemctl list-units –type=target
systemctl isolate multi-user.target
| Sysvinit Runlevel |
Systemd Target |
Function |
| 0 |
runlevel0.target, poweroff.target |
System halt/shutdown |
| 1,single,s |
System halt/shutdown |
Single-user mode |
| 2,4 |
runlevel2.target, runlevel4.target, multi-user.target |
User-defined/Site-specific runlevels. By default, identical to 3. |
| 3 |
runlevel3.target, multi-user.target |
Multi-user, non-graphical mode, text console only |
| 5 |
runlevel5.target, graphical.target |
Multi-user, graphical mode |
| 6 |
runlevel6.target, reboot.target |
Reboot |
| emergency |
emergency.target |
Emergency mode |
|
| Q007:-Disk have 5GB disk utilization even though files are unable to create, why?
(1)ACL
(2)inod
(3)over quata |
Q008:-sar command o/p?
using sar we can see cpu user system iowait steal idl process statistics in other word sar Collect report or save system activity information.
sar -bBcdqrRuvwWy -I SUM -I XALL -n ALL -P ALL CPU %user %nice %system %iowait %steal %idl
| 1 |
CPU usage: |
a. To get current CPU usage
# sar 2 10
# sar -p 2 10
# sar -P ALL 2 10b. To get the CPU usage for the previous date, consider 14th:
# sar -P ALL -f /var/log/sa/sa14c. To get the CPU usage for the 10th of the month, from 7 AM to 3 PM (i.e. specifying the time):
# sar -P ALL -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
| 2 |
Memory usage: |
a. To get current memory usage:
# sar -r 2 10b. To get the memory usage for the previous date, consider 14th:
# sar -r -f /var/log/sa/sa14c. To get the memory usage for the 10th of the month, from 7 AM to 3 PM (i.e. specifying the time):
# sar -r -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Swap usage: |
a. To get current swap usage:
# sar -S 2 10b. To get swap usage for the previous date, consider 14th:
# sar -S -f /var/log/sa/sa14c. To get swap usage for the 10th of the month, from 7 AM to 3 PM:
# sar -S -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Load Average: |
a. To get current load average stats:
# sar -q 2 10b. To get load average stats for the previous date, consider 14th:
# sar -q -f /var/log/sa/sa14c. To get load average stats for the 10th of the month, from 7 AM to 3 PM:
# sar -q -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Paging usage: |
a. To get current paging usage:
# sar -B 2 10b. To get paging usage for the previous date, consider 14th:
# sar -B -f /var/log/sa/sa14c. To get paging usage for the 10th of the month, from 7 AM to 3 PM:
# sar -B -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
IO usage: |
a. To get current IO usage:
# sar -b 2 10b. To get IO usage for the previous date, consider 14th:
# sar -b -f /var/log/sa/sa14c. To get IO usage for the 10th of the month, from 7 AM to 3 PM:
# sar -b -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Disk IO usage: |
a. To get current disk IO usage:
# sar -d -p 2 10b. To get disk IO usage for the previous date, consider 14th:
# sar -d -p -f /var/log/sa/sa14c. To get disk IO usage for the 10th of the month, from 7 AM to 3 PM:
# sar -d -p -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Networking stats: |
a. To get current network device stats:
# sar -n DEV 2 10b. To get network device stats for the previous date, consider 14th:
# sar -n DEV -f /var/log/sa/sa14c. To get network device stats for the 10th of the month, from 7 AM to 3 PM:
# sar -n DEV -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Power Management Stats: |
a. To get current power management usage:
# sar -m 2 10b. To get power management used for the previous date, consider 14th:
# sar -m -f /var/log/sa/sa14c. To get power management used for the 10th of the month, from 7 AM to 3 PM:
# sar -m ALL -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
|
Memory Stats (Page activities): |
a. To get current memory stats:
# sar -R 2 10b. To get memory stats for the previous date, consider 14th:
# sar -R -f /var/log/sa/sa14c. To get memory stats for the 10th of the month, from 7 AM to 3 PM:
# sar -R ALL -f /var/log/sa/sa10 -s 07:00:00 -e 15:00:00 |
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