Bash Index : L - The 'L' Bash commands : description, flags and examples

Create a new log entry :

logger 'hello world'

Find it :

journalctl -r _COMM=logger

-- Logs begin at Thu 2017-11-02 08:27:51 CET, end at Tue 2019-04-02 16:15:41 CEST. --
Apr 02 16:15:41 myLaptop bob[28892]: hello world

lastb is the same as last (lastb symlinks to /usr/bin/last), except that by default it shows a log of /var/log/btmp, which contains all the bad login attempts.

On Debian Wheezy, /var/log/btmp does not trace failed SSH login attempts. This is a known Debian bug, and has been fixed with OpenSSH package version 1:6.6p1-1 (source).

C.UTF-8
en_GB.UTF-8
en_US.UTF-8
fr_CA.UTF-8
fr_FR.UTF-8

• List of Locale Codes by country
• files :
  • /usr/share/i18n/SUPPORTED (source)
  • locale configuration file : /etc/locale.gen

C

• This is the standard C locale. The attributes and behavior it provides are specified in the ISO C standard. (source)
• The C locale is a special locale that is meant to be the simplest locale. You could also say that while the other locales are for humans, the C locale is for computers. In the C locale :
  • characters are single bytes
  • the charset is ASCII (well, is not required to, but in practice will be in the systems most of us will ever get to use)
  • the sorting order is based on the byte values
  • the language is usually US English
  • and things like currency symbols are not defined
  (source)

POSIX

• alias for the standard C locale (source)

export LANG="fr_FR.UTF-8"

During a PuTTY session, no effect as normal user, worked as root not in the current shell but in a new one.

The full error message was :

perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
	LANGUAGE = (unset),
	LC_ALL = (unset),
	LANG = "fr_FR.UTF-8"
	are supported and installed on your system.
perl: warning: Falling back to the standard locale ("C").

There may be unnecessary / overkill / wrong(?) steps in the solution below.

1. Contrary to popular belief, locale-gen takes NO argument (man locale-gen, if you don't believe me). So our first step is to select the locales we want by uncommenting them from /etc/locale.gen
2. Then rebuild locales : locale-gen
3. dpkg-reconfigure locales, leave everything as-is on the first page, then set the system language to en_US.UTF-8
4. export LANG="en_US.UTF-8"

unit : K
-rw------- 1 kevin users 12288 Mar 7 09:41 /tmp/tmp.NdDV69WZth	KiB : OK
unit : M
-rw------- 1 kevin users 12 Mar 7 09:41 /tmp/tmp.NdDV69WZth	MiB : OK
unit : G
-rw------- 1 kevin users 1 Mar 7 09:41 /tmp/tmp.NdDV69WZth		GiB : KO
unit : T
-rw------- 1 kevin users 1 Mar 7 09:41 /tmp/tmp.NdDV69WZth		TiB : KO

ls -l outputs things like :

-rw-------  1 bob    developers  4.0K Dec 16 18:20 myFile
-rw-------  1 bob    developers   280 Dec 16 17:30 myFileToo
drwx------  2 bob    developers  4.0K Dec 16 17:26 myDirectory
drwxrwxr-x+ 2 stuart otherGroup  4096 Dec 16 17:19 someOtherDirectory

drwxrwxr-x+ (source)

The single character following the file mode bits specifies which alternate access method (aka "system of permissions") applies to the file :

[SPACE]

no alternate access method, the regular Unix permissions apply

.

• file with a SELinux security context
• details : ls -Z myFile

+

any other combination of alternate access methods, very likely ACL

details : ls reports unexpected group permissions on files with ACL

-rw------- 1, drwx------ 2

number of hard links

• ls -Shl
• ll -Sh

ls is smart enough to sort files by size even though they are displayed in human-readable format.

• ls -l --time-style='+%d-%m-%Y %H:%M:%S' file
• ls -l --time-style='full-iso' file

• ls -ul --time-style='+%d-%m-%Y %H:%M:%S' file
• ls -ul --time-style='full-iso' file

-l causes the display of the total line. To workaround this, add -d * to your command : ls -ld *

1. create a playground
   tmpDir=$(mktemp -d); cd "$tmpDir"
2. create those files with unusual names
   touch aFilenameWithoutSpace 'a filename with spaces' $'a filename with space and\na newline'
3. what happens when we ls these files ?
   spacer='==========';
   echo "with 'ls -1' :"; ls -1;
   echo -e "$spacer\nwith 'ls | cat' :"; ls | cat;

   with "ls -1" :
   aFilenameWithoutSpace
   'a filename with space and'$'\n''a newline'ls looks smart enough to list 3 files
   'a filename with spaces'
   ============
   with "ls | cat" :
   aFilenameWithoutSpace
   a filename with space andls | cat is puzzled by the newline \n
   a newline
   a filename with spaces

4. more ?
   echo -e "$spacer\nwith 'for \$(ls)' :"; for i in $(ls); do ls "$i"; done;using ls inside loop to simulate a filesystem operation (copy, ...) on files
   echo -e "$spacer\nwith 'for \"\$(ls)\"' :"; for i in "$(ls)"; do ls "$i"; done;

   ==========
   with 'for  $(ls)' :
   aFilenameWithoutSpace
   ls: cannot access 'a': No such file or directory
   ls: cannot access 'filename': No such file or directoryHouston, we have a problem ! 
   ls: cannot access 'with': No such file or directory
   ls: cannot access 'space': No such file or directory
   ls: cannot access 'and': No such file or directory
   ls: cannot access 'a': No such file or directory
   ls: cannot access 'newline': No such file or directory
   ls: cannot access 'a': No such file or directory
   ls: cannot access 'filename': No such file or directory
   ls: cannot access 'with': No such file or directory
   ls: cannot access 'spaces': No such file or directory
   ==========
   with 'for  "$(ls)"' :
   ls: cannot access 'aFilenameWithoutSpace'$'\n''a filename with space and'$'\n''a newline'$'\n''a filename with spaces': No such file or directoryOoops 

5. even more ?
   for i in *; do echo "$i"; done; echo -e "$spacer"; for i in *; do ls "$i"; done

   aFilenameWithoutSpace
   a filename with space andthis is what loop items look like
   a newline
   a filename with spaces
   ==========
   aFilenameWithoutSpace
   'a filename with space and'$'\n''a newline'but that's very kind of ls
   'a filename with spaces'

6. workarounds :
   So far, I've found no workaround to handle files having a newline \n in their name.
   • that fail :
     • for i in $(find -type f); do echo "item : '$i'"; echo -n "seen by 'ls' : "; ls -1 "$i"; done

       item : './a'
       seen by 'ls' : ls: cannot access './a': No such file or directory
       item : 'filename'
       seen by 'ls' : ls: cannot access 'filename': No such file or directory
       item : 'with'
       seen by 'ls' : ls: cannot access 'with': No such file or directory
       

     • for i in "$(find -type f)"; do echo "item : '$i'"; echo -n "seen by 'ls' : "; ls -1 "$i"; done

       item : './a filename with space and
       a newline
       ./a filename with spacesthe 3 file names are concatenated into a single value because of quotes : "$(find -type f)"
       ./aFilenameWithoutSpace'
       seen by 'ls' : ls: cannot access './a filename with space and'$'\n''a newline'$'\n''./a filename with spaces'$'\n''./aFilenameWithoutSpace': No such file or directory

     • while read i; do echo "item : '$i'"; echo -n "seen by 'ls' : "; ls -1 "$i"; done < <(find -type f)

       item : './a filename with space and'
       seen by 'ls' : ls: cannot access './a filename with space and': No such file or directoryKO with newline \n
       item : 'a newline'
       seen by 'ls' : ls: cannot access 'a newline': No such file or directory
       item : './a filename with spaces'
       seen by 'ls' : './a filename with spaces'OK with spaces
       item : './aFilenameWithoutSpace'
       seen by 'ls' : ./aFilenameWithoutSpace

   • that work :
     • find -type f -exec ls -1 {} +

       ./aFilenameWithoutSpace
       './a filename with space and'$'\n''a newline'
       './a filename with spaces'

     special case : when there is no file matching the search criteria :
     for i in path/to/files/*xyz; do ls "$i"; done
     ls: cannot access 'path/to/files/*xyz': No such file or directory
     
     for i in $(find path/to/files -iname "*xyz"); do ls "$i"; done
     (nothing)

7. clean playground and leave :
   cd "$tmpDir/.." && [ -d "$tmpDir" ] && rm -rf "$tmpDir"

Flag	Usage
+F	Follow file contents in real time, like tail -f does : less +F myFile
-i	make further searches case-insensitive provided the search pattern is all lowercase !
-N --LINE-NUMBERS	show line Numbers For some (unknown so far) reason, those extra line numbers can not be matched after a | : echo -e "apple\nbanana" | less -N 1 apple 2 banana echo -e "apple\nbanana" | less -N | grep a apple banana echo -e "apple\nbanana" | less -N | grep 1 (nothing but "FAILURE" return code) echo -e "apple\nbanana" | less | sed -n '/a/ p' apple banana echo -e "apple\nbanana" | less -N | sed -n '/a/ p' apple banana echo -e "apple\nbanana" | less -N | sed -n '/1/ p' (nothing but "SUCCESS" return code)
-ppattern --pattern=pattern	start at the first occurrence of pattern in the file
-R	interpret ANSI color escape sequences Outsmarted by GNU/Linux utilities and the shell (details) : by default, less does not interpret color codes utilities —such as grep & al.— are smart enough not to send color codes when piping their output to less As a result, if you want colors, you'll have to be explicit with both and instruct : utilities to output color codes —even though these are piped to less less to interpret these codes grep --color=always searchPattern myFile | less -R
-S --chop-long-lines	show the portion of a long line that doesn't fit the screen width on the next line chop long lines in interactive mode

Flag	Usage
F	Follow file contents in real time, like tail -f does
g ng	jump to beginning of line jump to line n
G	jump to end of line
- i	toggle case sensitivity in searches (by default, searches are case-sensitive, so this will turn them case-insensitive at first strike)
n	jump to next match
N	jump to previous match
v	edit the current file with the editor defined in the EDITOR environment variable
:-n	display the next file (when less is launched like : less *conf)
:-p	display the previous file (when less is launched like : less *conf)
&RegExp	show lines matching RegExp. Back to normal (display all lines ) : &
/pattern	search forward pattern (see also)
?pattern	search backward pattern
= : f Ctrl-g	display information about the file being viewed : line range currently on screen / total line number byte offset / file size (aka byte count) point in file as percentage

- - c h

Objects to list	Matching condition	Command
processes	related to TCP daemons UDP daemons	lsof -i tcp lsof -i udp
processes	related to a web server	lsof -i tcp:80
processes	using TCP port 80 on the 127.0.0.1 interface	lsof -i 4tcp@127.0.0.1:80
network connections	between localhost and 1.2.3.4	lsof -i @1.2.3.4
network connections	related to the process having PID 1234	lsof -a -i -p 1234
files	opened by kevin or by whoever has the 500 UID or by PID 123 or by PID 456	lsof -u kevin,500 -p 123,456

• lsof -nP | grep deleted
• or : lsof +L1
• sort files by increasing size : lsof +L1 | sort -k7 -n

COMMAND     PID     USER   FD   TYPE DEVICE SIZE/OFF NLINK     NODE NAME
chrome    70803 stuart   50u   REG   0,28        4     0    12443 /dev/shm/.org.chromium.Chromium.wo6MuZ (deleted)
teams      3837 stuart   67u   REG  253,1       16     0 31326254 /tmp/skype-3837/skypert_sessionkeyY9CXIY (deleted)

firefox    3243 stuart   48r   REG    0,1     2356     0     6155 /memfd:mozilla-ipc (deleted)
Thunar     2830 stuart   26r   REG  253,1    27812     0 19136866 /home/stuart/.local/share/gvfs-metadata/root (deleted)
firefox    3243 stuart  235r   REG  253,1    32768     0 19136838 /home/stuart/.local/share/gvfs-metadata/home-bbf7c99f.log (deleted)
panel-5-n  2853 stuart   13r   REG  253,1    32768     0 19136749 /home/stuart/.local/share/gvfs-metadata/home-80f437a6.log (deleted)
Thunar     2830 stuart   27r   REG  253,1    32768     0 19136918 /home/stuart/.local/share/gvfs-metadata/root-7816e02b.log (deleted)
firefox    3243 stuart   50r   REG    0,1    64150     0     6156 /memfd:mozilla-ipc (deleted)
teams      3667 stuart   40u   REG   0,28    65536     0       14 /dev/shm/.org.chromium.Chromium.xi0O84 (deleted)

teams      3853 stuart   54u   REG   0,28  4198400     0      768 /dev/shm/.org.chromium.Chromium.mbVPNT (deleted)
chrome    71055 stuart   46u   REG   0,28 16777216     0    17328 /dev/shm/.org.chromium.Chromium.q7zzD0 (deleted)
pulseaudi  2428 stuart    6u   REG    0,1 67108864     0     1028 /memfd:pulseaudio (deleted)

These files have been marked as deleted but the storage space they use has not been freed yet because they are still used by one or more processes. To free the space used by any of these files, you just have to stop/restart the process holding it.
For details on any of these "almost deleted" files, have a look at /proc/PID/fd/FD (FD : digits only, no trailing letter). To recover one of them, just read below.

"Deleted" files can be the reason why a volume is reported as full whereas ls, df and du report there is some space left.

This can be used to recover "almost deleted" files :

lsattr myFile

------------- myFile

lsattr -d myDirectory

------------- myDirectory