user1046658's questions

I want to grep for a variable that has the string test, but I also want to make sure that it will only find test if that is the only word on a line.

So, I tried this:

string=test
echo "test" | grep "$string$"

I would like to know if grep knows that the first part, $string (in grep "$string$"), is asking to find for the string test, while the last part, $ (in grep "$string $" is asking to find for test, but nothing should be after test in the line. Is grep able to distinguish $string as a variable and only $ as the regex for end of the line, or do I have to use a certain way to distinguish them apart?

I have a string like: testfsdfsdftestfsdkflsdtestsdfsdfsdf

I am wondering how to separate the string so that testfsdfsdf appears on the first line, testfsdkflsd will appear on the second line, etc. like this:

testfsdfsdf
testfsdkflsd
testsdfsdfsdf

I tried using sed to find test and anything after it with sed 's/test.*/ but I am wondering how to reprint test.* again. From what I know with sed, you can use it to find a particular string and then replace it with something else. So essentially, I wanted to try something like sed 's/test.*/[reprint test.* here]\n/g', but if I do sed 's/test.*/test.*\n/g', it just outputs test.*. Is there any way I can reprint the string found with sed, or can this be done with another command?

I also tried sed 's/\(test.*\)test/\1\ntest/g', which works if there are only two instances of test[random characters], but not three or more. With the string testfsdfsdftestfsdkflsdtestsdfsdfsdf, it only prints:

testfsdfsdftestfsdkflsd
testsdfsdfsdf

I know sysctl [variable] such as sysctl vm.swappiness will print out the value of vm.swappiness. But when I tried sysctl vm.swappiness=10 and then typed sysctl vm.swappiness, it showed that vm.swappiness = 10 (it was 60 before). I thought to change a sysctl setting, you had to do sysctl -w [variable] such as sysctl -w vm.swappiness=10.

Is there a difference between sysctl vm.swappiness=10 and sysctl -w vm.swappiness=10?

I thought that sysctl -w vm.swappiness=10 might edit /etc/sysctl.conf directly, but that does not seem to be the case because when I entered sysctl -w vm.swappiness=10 and then looked at /etc/sysctl.conf, vm.swappiness was still set to 60. Then, when I did sysctl -p, vm.swappiness became 60 again.

So additionally, does sysctl -w configure /etc/sysctl.conf in any way?

When I use gedit in Ubuntu 20.04, whenever I click on any of the checkboxes in Preferences, nothing happens.

For example, when I click on Display line numbers, the checkbox is still marked as checked. For some reason, clicking Display grid pattern, Enable text wrapping, and Do not split words over two lines works, but when I exit out of Preferences and come back in, they go back to their original status, as shown in the picture.

All other options in other tabs can not be changed.

Edit: Apparently Preferences works when using gedit as a normal user, and not root. Previously, I was trying to change the Preferences as root

Now, I wonder why Preferences can not be changed as root. I noticed that when I use gedit as a normal user, nothing pops up at the terminal, but when I open gedit as root, the following message is displayed in the terminal:

(gedit:2024): dconf-WARNING **: 21:01:08.260: failed to commit changes to dconf: The connection is closed

(gedit:2024): dconf-WARNING **: 21:01:08.270: failed to commit changes to dconf: The connection is closed
Error creating proxy: The connection is closed (g-io-error-quark, 18)
Error creating proxy: The connection is closed (g-io-error-quark, 18)
Error creating proxy: The connection is closed (g-io-error-quark, 18)
Error creating proxy: The connection is closed (g-io-error-quark, 18)
Error creating proxy: The connection is closed (g-io-error-quark, 18)

(gedit:2024): dconf-WARNING **: 21:01:08.509: failed to commit changes to dconf: The connection is closed

(gedit:2024): dconf-WARNING **: 21:01:08.509: failed to commit changes to dconf: The connection is closed

(gedit:2024): dconf-WARNING **: 21:01:08.510: failed to commit changes to dconf: The connection is closed
XDG_RUNTIME_DIR (/run/user/1000) is not owned by us (uid 0), but by uid 1000! (This could e.g. happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)
XDG_RUNTIME_DIR (/run/user/1000) is not owned by us (uid 0), but by uid 1000! (This could e.g. happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)

(gedit:2024): dconf-WARNING **: 21:04:00.840: failed to commit changes to dconf: The connection is closed
XDG_RUNTIME_DIR (/run/user/1000) is not owned by us (uid 0), but by uid 1000! (This could e.g. happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)
XDG_RUNTIME_DIR (/run/user/1000) is not owned by us (uid 0), but by uid 1000! (This could e.g. happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)

I am using Ubuntu 16.04.

I want to search for a certain word, but I also want the whole file that contains the word to be outputted on the terminal so that I can see where in the file the word is located. However, when I use grep, it will only show the particular sentence that contains the word, not the whole file.

What command can I use to search for a word but also show the whole file along with the place where the word is located?

I am trying to use SquirrelMail on Ubuntu 16.04.

When I go to localhost/squirrelmail/src/login.php and login, I encounter the error message: ERROR: Connection dropped by IMAP server.

I tried the solution here, which says to add in /etc/dovecot/dovecot.conf:

protocol imap {
mail_location = mbox:~/mail:INBOX=/var/mail/%u
}

but the error persists.

Additionally, I tried the solution here, which informs to add in /etc/dovecot/dovecot.conf:

namespace inbox {
    inbox = yes
}

but again, the error persists.

My /etc/dovecot/dovecot.conf file is:

## Dovecot configuration file
# If you're in a hurry, see http://wiki2.dovecot.org/QuickConfiguration
# "doveconf -n" command gives a clean output of the changed settings. Use it
# instead of copy&pasting files when posting to the Dovecot mailing list.
# '#' character and everything after it is treated as comments. Extra spaces
# and tabs are ignored. If you want to use either of these explicitly, put the
# value inside quotes, eg.: key = "# char and trailing whitespace  "
# Most (but not all) settings can be overridden by different protocols and/or
# source/destination IPs by placing the settings inside sections, for example:
# protocol imap { }, local 127.0.0.1 { }, remote 10.0.0.0/8 { }
# Default values are shown for each setting, it's not required to uncomment
# those. These are exceptions to this though: No sections (e.g. namespace {})
# or plugin settings are added by default, they're listed only as examples.
# Paths are also just examples with the real defaults being based on configure
# options. The paths listed here are for configure --prefix=/usr
# --sysconfdir=/etc --localstatedir=/var
# Enable installed protocols
!include_try /usr/share/dovecot/protocols.d/*.protocol
# A comma separated list of IPs or hosts where to listen in for connections. 
# "*" listens in all IPv4 interfaces, "::" listens in all IPv6 interfaces.
# If you want to specify non-default ports or anything more complex,
# edit conf.d/master.conf.
#listen = *, ::
# Base directory where to store runtime data.
#base_dir = /var/run/dovecot/
# Name of this instance. In multi-instance setup doveadm and other commands
# can use -i <instance_name> to select which instance is used (an alternative
# to -c <config_path>). The instance name is also added to Dovecot processes
# in ps output.
#instance_name = dovecot
# Greeting message for clients.
#login_greeting = Dovecot ready.
# Space separated list of trusted network ranges. Connections from these
# IPs are allowed to override their IP addresses and ports (for logging and
# for authentication checks). disable_plaintext_auth is also ignored for
# these networks. Typically you'd specify your IMAP proxy servers here.
#login_trusted_networks =
# Space separated list of login access check sockets (e.g. tcpwrap)
#login_access_sockets = 
# With proxy_maybe=yes if proxy destination matches any of these IPs, don't do
# proxying. This isn't necessary normally, but may be useful if the destination
# IP is e.g. a load balancer's IP.
#auth_proxy_self =
# Show more verbose process titles (in ps). Currently shows user name and
# IP address. Useful for seeing who are actually using the IMAP processes
# (eg. shared mailboxes or if same uid is used for multiple accounts).
#verbose_proctitle = no
# Should all processes be killed when Dovecot master process shuts down.
# Setting this to "no" means that Dovecot can be upgraded without
# forcing existing client connections to close (although that could also be
# a problem if the upgrade is e.g. because of a security fix).
#shutdown_clients = yes
# If non-zero, run mail commands via this many connections to doveadm server,
# instead of running them directly in the same process.
#doveadm_worker_count = 0
# UNIX socket or host:port used for connecting to doveadm server
#doveadm_socket_path = doveadm-server
# Space separated list of environment variables that are preserved on Dovecot
# startup and passed down to all of its child processes. You can also give
# key=value pairs to always set specific settings.
#import_environment = TZ
##
## Dictionary server settings
##
# Dictionary can be used to store key=value lists. This is used by several
# plugins. The dictionary can be accessed either directly or though a
# dictionary server. The following dict block maps dictionary names to URIs
# when the server is used. These can then be referenced using URIs in format
# "proxy::<name>".
dict {
  #quota = mysql:/etc/dovecot/dovecot-dict-sql.conf.ext
  #expire = sqlite:/etc/dovecot/dovecot-dict-sql.conf.ext
}
# Most of the actual configuration gets included below. The filenames are
# first sorted by their ASCII value and parsed in that order. The 00-prefixes
# in filenames are intended to make it easier to understand the ordering.
!include conf.d/*.conf
# A config file can also tried to be included without giving an error if
# it's not found:
!include_try local.conf

My /etc/postfix/main.cf is:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version
# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
# appending .domain is the MUA's job.
append_dot_mydomain = no
# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h
readme_directory = no
# TLS parameters
smtpd_tls_cert_file = /etc/postfix/ssl/mailserver.crt
smtpd_tls_key_file = /etc/postfix/ssl/mailserver.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = ubuntu-vm.localdomain
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = $myhostname, localhost, ubuntu-vm, localhost.localdomain, localhost
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all
smtpd_sasl_local_domain = 
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtp_tls_security_level = may
smtpd_tls_security_level = may
smtpd_tls_auth_only = no
smtp_tls_note_starttls_offer = yes
smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem
smtpd_tls_loglevel = 1
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom
localhost = example.com

In addition, I went to localhost/squirrelmail/src/configtest.php and received:

SquirrelMail configtest
This script will try to check some aspects of your SquirrelMail configuration and point you to errors whereever it can find them. You need to go run conf.pl in the config/ directory first before you run this script.
SquirrelMail version:   1.4.23 [SVN]
Config file version:    1.4.0
Config file last modified:  01 July 2020 20:51:58
Checking PHP configuration...
    PHP version 7.0.33-0ubuntu0.16.04.15 OK.
    Running as www-data(33) / www-data(33)
    display_errors:
    error_reporting: 22527
    variables_order OK: GPCS.
    PHP extensions OK. Dynamic loading is disabled.
    ERROR: You have configured PHP not to allow short tags (short_open_tag=off). This shouldn't be a problem with SquirrelMail or any plugin coded coded according to the SquirrelMail Coding Guidelines, but if you experience problems with PHP code being displayed in some of the pages and changing setting to "on" solves the problem, please file a bug report against the failing plugin. The correct contact information is most likely to be found in the plugin documentation.
Checking paths...
    Data dir OK.
    Attachment dir OK.
    Plugins OK.
    Themes OK.
    Default language OK.
    Base URL detected as: http://localhost/squirrelmail/src (location base autodetected)
Checking outgoing mail service....
    SMTP server OK (220 ubuntu-vm.localdomain ESMTP Postfix (Ubuntu))
Checking IMAP service....
    IMAP server ready (* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN] Dovecot ready.)
    Capabilities: * CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE AUTH=PLAIN
Checking internationalization (i18n) settings...
     gettext - Gettext functions are available. On some systems you must have appropriate system locales compiled.
     mbstring - Mbstring functions are unavailable. Japanese translation won't work.
     recode - Recode functions are unavailable.
     iconv - Iconv functions are available.
     timezone - Webmail users can change their time zone settings.
Checking database functions...
    not using database functionality.
Congratulations, your SquirrelMail setup looks fine to me!
Login now

I ran echo "\oo" | tr "\oo" " ", and the output is:

\

\o is not a special character, like \n, so why is the \ not converted into a space too?

In the manpage for nc -l, it says:

It is an error to use this option in conjunction with the -p, -s, or -z options.

But most examples I see online using this command use nc -lp [port].

Can you use -p with -l in nc? And with just nc -l [port], is that the correct usage of it because when I connect to it on another terminal with nc [ip address] [port], it works. Also, when I use nc -lp [port] and connect to it with nc [ip address] [port], it also works. Is there a difference between these two commands?

With the commands systemctl start apache2 and systemctl start apache2.service, is there any difference between them?

What does the .service mean? Does it do anything that systemctl start apache2 does not?

Or is apache2 just the shortened version of apache2.service?

In find -name "*.mp3", there is an asterisk before the .mp3. Doesn't the * match the character before it any number of times? But there is nothing in front of the asterisk, so what does the * do? Or is it because the find command does not use regular expressions? So, is the . in .mp3 a regular expression character or does find just interprets it as a period to match?

The iptables manual page for -m, --match match is:

Specifies a match to use, that is, an extension module that tests for a specific property. The set of matches make up the condition under which a target is invoked. Matches are evaluated first to last as specified on the command line and work in short-circuit fashion, i.e. if one extension yields false, evaluation will stop.

I do not understand what this means, specifically, what does the extension module mean?

Also, how is iptables -A INPUT -m tcp ... different from iptables -A INPUT -p tcp ... ?

I read that grouping treats an expression as a single unit. What does that mean?

Furthermore, what does grep "\(grouping\)" file.txt or grep -E "(grouping)" file.txt do? I also read that expressions are grouped with parenthesis. Again, what is grouping expressions?

When I run the command, it highlights grouping in the file. How is grep "\(grouping\)" different from grep grouping?

What does "<" do in iptables-restore < [file]?

Additionally, what does this command do? Does it change the file?

Are there other commands or ways to use "<"?

I saw the command sudo apt-get update --dry-run which apparently said it should give the number of packages that need updates. However, when I run it on Ubuntu 16.04, I get E: Command line option --dry-run is not understood in combination with the other options.

What is the right command that will give the number of updates, preferably similar to sudo apt-get update --dry-run?

There was a command I found explaining the ls -l command, and it gave an example as ls -l /boot/. I find that ls -l /boot and ls -l /boot/ have the same results. Does /boot and /boot/ have any differences? What does the / after boot (/boot /) mean in contrast to /boot without a / after boot?

I created a file called test and gave it the permissions ----rwxrwx or 077. The owner of test is a user called user and the group owner is root. user is not in the group root. The 7 in 077 means that all other people can read, write, and execute the file. When I log in as user, I can not read, write, or execute test.

Also, when I change test's permission to -rwx---rwx or 707 and change the owner to root and group owner to user, when I log in as user, I can not read, write, or execute test.

Is this because the 'all other people' section in 077 in the permissions do not include the owner or the group owner? Because if it does include the owner and the group owner, wouldn't the owner and the group owner be able to change the file even if their permission as owner or group owner is set to --- or 0?

I am using Ubuntu 16.04

I am in the root user and typed the command:

usermod -d /home test

I believe this changes the default location of test's home directory to /home. But then when I log into the user, test, the screen goes black and returns to the login screen.

I then go back to my account, and as root, typed the command:

usermod -d /home/test test

/home/test was the original default directory for test.

And then I log into the user test, and I log in successfully.

Why does this happen? What can I do in order to change the default directory of test but not meet a login loop?

I am using Ubuntu 18.04.

I used the command

usermod -e YYYY_MM_DD user

Now, the user's account is expired.

What command can I put in order to remove the expiration date on the user account?