Stop using tail -f (mostly)

http://www.brianstorti.com/stop-using-tail/?utm_content=buffer13c97&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

by Pdincau • 11 years ago

765 207 11 years ago

brianstorti.com

BrandonBradley• 11 years ago

Good share! Command line fu is always nice.

jaryd• 11 years ago

I just tried this on an extremely active logfile and it didn't work very well for me. I'd recommend multitail for watching constantly changing files.

_RPM• 11 years ago

tail works best for me. I'm not going stop using it just because a person on the internet says not to.

TorKlingberg• 11 years ago

The title is a bit clickbaity, but ignore that and it's a useful tip you might not know. The author doesn't actually demand you stop using tail -f if you like it better.

jabo2• 11 years ago

I use tail -f and when I need to search, I use iTerm's search (Cmd+F) which highlights matches and even supports regex. I also have an unlimited scroll buffer so I can just scroll up or down to get the context of a particular match.

varikin2• 11 years ago

That only works if you only care about search results since you started tailing. If you want to search for what happened before you started tailing, you need to stop tailing and use less/grep/etc.

jabo2• 11 years ago

Ah yes. I usually let the tail -f run, open another SSH session and grep from there.

mason55• 11 years ago

This only works if what you are searching for has scrolled past since you started following. If you want to see other occurrences in the file you're out of luck. For example, let's say you are watching to see which error message is generated when something goes wrong, then you want to see when else that error message has been thrown.

tikums• 11 years ago

Or use multitail. It supports syntax highlighting, among other features: http://www.vanheusden.com/multitail/

drzaiusapelord• 11 years ago

multitail is great. I really cannot use command line utils that don't support colors/highlighting anymore. htop instead of top, etc. It just gives me much better visibility and readability. I'm surprised that so many non-color utils are still being used. It just feels so 1994 to me to stare at a white on black display. I guess there's nothing more slow moving and conservative than shell interfaces, thus articles like these that shame us into using different tools.

Personally, I'd love to see some hot young talent just do a 100% redo of the standard gnu utils from an interface perspective. Just go crazy with new interface and display ideas, novel presentation modes, novel navigation, etc while still maintaining backwards compatibility. I could see a big disruption here.

0x0• 11 years ago

Also take a look at ccze which is great for syntax-coloring all kinds of log files heuristically.

For example: tail -F somefile.log|ccze -A

For your shell, there's a lot of funky colorful interactive customizations you can get on zsh and fishfish.

smorrow• 11 years ago

I use htop and turn the colours off... thing I like about htop is I can use the mouse. It's so F-key-based, which, especially on a laptop, means you have to take your eyes off the screen to find the keys.

Of course, I'm not opposed to colours, I'm opposed to colours that look tacky / l33t hax0r, which would be most terminal stuff. I like 𝐛𝐨𝐥𝐝 better than trying to find colours I won't hate.

freehunter2• 11 years ago

Switching between many programs and systems, I have a hard time keeping track of what colors mean what. Especially when people start customizing their colors. There are enough tools to show you what a file is, I don't need directories printed in red and files in blue and symlinks in green. ls -l is good enough and works everywhere.

cromo• 11 years ago

I wrote a Python script (called synesthesia)[1] that'll colorize input based on regex matches, and any matched text will be the same color for the same content.

The use case that drove its development was needing to keep track of UUIDs across multiple logs - and grep --color will colorize its matches, but not differentiate between ones that have different content. With this, I could watch both logs as data was passed from one to the other and keep track of e.g. the orange one.

I also thought it would be nice to be able to use patterns from logstash's grok, so I wrote grokpat[2] to find patterns for me. A lot of grok's patterns use atomic groups, which aren't available in Python 2, so I wrote redi[3] to convert them from grok's syntax to Python compatible syntax.

So I can now colorize logs easily as follows:

  tail -F program.log | synesthesia "$(redi "$(grokpat uuid)")"

[1] https://github.com/cromo/synesthesia [2] https://github.com/cromo/grokpat [3] https://github.com/cromo/redi

scrame2• 11 years ago

This _almost_ touches on the useful part of this: If you search in less and then put it in follow mode, it continues to highlight the search terms. This is very useful for trapping an exception or webcall in the wild.

The downside: less buffers and tail -f prints directly. On a slow printing log this can cause events to show up slowly, and can cause performance issues on a fast moving log. If you're piping through a script for processing, tail -f is still the best bet. If you need multiple files, multitail is probably better. less +F hits a quick+easy operational niche and is available almost everywhere (whereas multitail is not).

bch5• 11 years ago

+1 (upvoted).

$ less ./somefile

  /somesearch^M (<--- does a search)
  F             (<--- puts less(1) in "follow mode", highlighting your previous search-term if it occurs in the future)

(Edit: formatting)

wampus2• 11 years ago

But how do you combine the two on the command line, so less is tailing the file AND highlighting a pattern when launched?

I typically read logfiles with less +F, but it would be nice to create an alias for patterns in specific types of logs, so I don't have to remember them or rely on command history.

twic• 11 years ago

The other useful thing is filtering - on sufficiently modern versions of less [1], you can use & to filter the lines, in the same way you use / to search them - only lines matching the filter are shown, and the display continues to update. Use &! for a negative filter. This has replaced grep | tail for me, with the advantage that it's non-destructive, so you can undo the filter, reapply a different one, etc.

[1] Everything i've used on Linux in the last few years, not the vanilla one on the Mac, but the one in Homebrew

barrkel• 11 years ago

& is very handy, however it is also excruciatingly slow. It looks like it uses an O(n^2) algorithm, just from observing how slow it works.

dredmorbius4• 11 years ago

I was going to mention multitail as well, which is a fantastic utility. That and rsstail, both by Folkert Van Heusden, are quite slick. The mark it leaves (a red line across the screen) is even more visible than those given by less.

I've commented a bit more on them (in the context of other RSS tools) here:

https://www.reddit.com/r/dredmorbius/comments/1udv6i/further...

Folkert's site: http://www.vanheusden.com/ http://www.vanheusden.com/multitail/ http://www.vanheusden.com/rsstail/

Though not quite applicable to logfiles, I've written a script to tail my Newsbeuter feed URLs with Multitail support, for a console / terminal-based RSS feed.

tom-lord• 11 years ago

You can also achieve this by doing:

tail -f whatever.log | grep --color=auto -C99 exception

And there are other ways pausing/scrolling back, such as tmux's scroll mode.

nothrabannosir• 11 years ago

Even when you don't want less +F, a good alternative to tail -f is tail -F. It survives log rotation, and the file being temporarily inaccessible:

    --retry
	      keep trying to open a file even if it is inaccessible when  tail
	      starts  or if it becomes inaccessible later; useful when follow-
	      ing by name, i.e., with --follow=name

    -F        same as --follow=name --retry

varikin2• 11 years ago

This is my standard now. Logs rotate all the time and it very convenient to have tail continue working without my intervention.

pimlottc3• 11 years ago

+1 for -F. Note that --follow and --retry are gnuisms, while -F works on most implementations of tail (even though it's not part of POSIX).

fweespeech2• 11 years ago

Yeah, tail -F is the way to go imo.

Also, if you are using a proper ssh client, opening a second ssh connection to manage the reacting to the log files is habit for me at this point. The only time I'm using tail -F is after a new configuration deployment. Otherwise, I'm looking at archival data in ELK.

noddingham• 11 years ago

Have you tried using screen[1]? Might make things a little easier than have two separate SSH connections.

[1] https://www.gnu.org/software/screen/

protomyth4• 11 years ago

on OpenBSD -f does:

  Do not stop when end-of-file is reached, but rather to wait for
  additional data to be appended to the input.  If the file is re-
  placed (i.e., the inode number changes), tail will reopen the
  file and continue.  If the file is truncated, tail will reset its
  position to the beginning.  This makes tail more useful for
  watching log files that may get rotated.  The -f option is ig-
  nored if the standard input is a pipe, but not if it is a FIFO.

So, no -F or --retry but a different default behavior

acdha5• 11 years ago

Is there a bug report open for that yet? FreeBSD has this so they should be able to resync easily enough

nmc• 11 years ago

Huge caveat: "less +F" does not work with multiple files.

Yes, this is mentioned in the post, but I feel it is so big it would have deserved large, bold letters.

pimlottc3• 11 years ago

I was introduced to less +F a while ago and it is quite nice, but there is one simple "feature" of tail -f that I miss quite a lot: being able 'mark' the log with gaps by hitting enter a few times. This is especially handy when you have to first load a page or warm up the app before performing the operation you're interested in watching, letting you separate the earlier output from the lines generated by what you're testing.

With less, you have to keep track of the current position by timestamp or other unique message, and it's easy to lose your place when the output starts streaming in. With tail, you only need a moment to mark your spot and then it's visually distinct even as more message come in.

evincarofautumn• 11 years ago

With less, you can use m<letter> to mark the current position and '<letter> to go to a marked position. h will show you lots of useful help.

jimktrains2• 11 years ago

GP isn't meaning it like that, they mean being able to add some spaces so that the next log entries stand out for quick visual identification as you're making changes and reloading the application.

bch5• 11 years ago

An example of some of the vi commands that less(1) has adopted. You can also:

  * page forward and backward, including using numeric prefixes to indicate a lineno or indicate "repeat 'n' times".
  * launch vi if less(1) is working on a file (versus (eg) stdout of some process)
  * search fwd/backward
  * start examining a new file w/o leaving less(1)
  * ...

alinspired• 11 years ago

If you're using screen/tmux as myself, tail -f remains a good option, as you can enter gaps or search, or do 1000 more things as compared to plain terminal session

jmathai• 11 years ago

On OSX/iterm you can do command+k to clear the screen and less lets you navigate up if you need.

warrenm• 11 years ago

That doesn't change the actual log file, however - it's only visual whilst in the screen buffer

stonogo• 11 years ago

Be very, very careful with this: http://seclists.org/fulldisclosure/2014/Nov/74

But really, it's 2015. Are you really using a terminal emulator without a buffer search? Are you not using screen or tmux, both of which can do these things natively, with no external tools? Why? And what is wrong with backgrounding the tail command, running your grep, and then foregrounding the tail command?

Filligree• 11 years ago

Personally? The reason I'm not using screen is that there's no way to atomically [attach, create new window] in screen and I value my gnome-terminal tabs.

If tmux can do that, then I'd consider it reason to switch.

yellowapple• 11 years ago

Do you mean creating a new window every time you attach to an existing session? Or do you mean that each of those actions ("attach" and "create new window") should be atomic?

vacri• 11 years ago

Check out 'byobu'. Stupid name, but it's built on screen and can use the screen commands. Byobu has F2 for new terminal tab, F3/4 to shuffle between them.

philsnow2• 11 years ago

Depending on what you mean by "atomic" (do you really mean atomic, or do you just not want to have to type anything after you've attached to create the new window?), you can do this with screen's -X option. If that's what you want to do I can try to dig up the way I used to do this.

gitaarik2• 11 years ago

It's a nice feature of less, but less is a pager, so you can't pipe the result to `grep` or `sed` or `awk` or something.

nilkn• 11 years ago

I'd wager that 90% of the time that I'm using 'tail -F' I'm also piping it to grep.

jfroma2• 11 years ago

This. I use:

tail -f /var/log/x.log | grep foo -A 20 -B 20

Most of the time.

mattikus• 11 years ago

While you may not be able to do transforms on the output via `sed` or `awk`, you can get a grep-like filtering by using the `&` character with `less` open.

pcwalton• 11 years ago

less is my favorite text editor. It's a pity it doesn't actually edit text.

soyuka2• 11 years ago

You should try vim dude.

orthecreedence• 11 years ago

I use tail -f with tmux usually. Will less +F save the entire output into memory? In other words, if I accidentally leave it open in a tmux shell and the log grows to 300mb of output, will the server start swapping?

kragen4• 11 years ago

I usually run `less` niced and with a ulimit of 30 megabytes, but `less` also has an option to configure how much buffer space to use. As far as I can tell, the default is "all of your memory", which is a suboptimal default in my book.

simgidacav3• 11 years ago

That's an important point: never use this trick with huge logs...

mrinterweb• 11 years ago

One advantage that tail -f has is that you can insert newlines or other characters into the output to help you visually split log entries. Log files often look the same so being able to visually split up the log is very helpful IMO.

spatz• 11 years ago

The problem is that less +F polls every second while tail -f uses inotify, which is both more efficient and responds faster to change.

Florin_Andrei• 11 years ago

There was a time when tail didn't know inotify. It was so, so much better when it learned that trick.

There was also a time when there was a utility called inotail, bridging that gap until tail proper was improved. I very much preferred it over regular tail.

haberman2• 11 years ago

I always thought it was such a shame that you couldn't use plain poll() for this. poll()-ing on a read fd at EOF for a regular file should work like poll()-ing a network socket.

ekimekim• 11 years ago

The problem is in what concepts are being considered "the same" when mapping two mostly-dissimilar things (a socket or pipe, vs a file).

poll(), select() et al don't define "readable" as meaning "a byte of data is available". They define it as "read() will not block".

When you read to the end of a file, read() returns "". This is the same as when you try to read from a closed socket. Conceptually, they are linking the concepts of "EOF" and "closed", not the concepts of "EOF" and "waiting for data". And indeed, if you call poll() on a socket that has been closed on the remote end, you will find it is "readable".

Ultimately, regular files just were never intended to be used as pipes. The abstractions just weren't chosen to work in that way.

stass• 11 years ago

You can use kqueue/kevent to poll on a file. That's what tail(1) and other system utilities are using.

karlgoldstein• 11 years ago

Or just tail -f in an emacs buffer

VLM• 11 years ago

You mean like in multiterm or something? I guess so. In emacs there are always many ways to do things, which is awesome.

You can also open the file and engage auto-revert-mode or auto-revert-mode-tail. In my status bar it shows up as ARev mode.

Also you can bind those to your auto-mode-alist so all .log files get the tail treatment or whatever.

Scrolling can get weird.

Theres some google-able settings for the timeout to revert, default is about a sip of water (a few seconds?) but I guess you could crank it down to 1 second or something.

I like doing this in emacs so its all in the same ecosystem, if I need to cut and paste something weird to test it or put the message into code or even more likely to cut and paste actual error messages into docs or comments, I can do it inside emacs.

shabble• 11 years ago

It looks like from ~24.4 onwards there's support for various notification event sources for auto-revert[-tail]-mode, as determined by the file-notify--library variable. I don't appear to have anything compiled into my prebuilt OSX emacs though, time to update the ol' source tree and see if I can remember how to build it.

oimaz2• 11 years ago

less +F is not such a good alternative to "tail -f" or better "tail -F" especially when you are filtering the output of tail using grep or awk.

rcthompson• 11 years ago

I imagine you could probably do "tail -f | grep/awk ... | less +F".

simgidacav3• 11 years ago

It works fine indeed. I'm using it all the time.

jcfrei• 11 years ago

The biggest nag I have with tail is that it stops tracking a file once it gets moved and a new one is created in its place (through log rotation).

vially• 11 years ago

As mentioned by others in this thread, you can use: "tail -F data.log"

emilsedgh• 11 years ago

For lazy people out there:

There is also the command `tailf` which is quite similar to 'tail -f'.

2 characters make so much difference :)

colechristensen• 11 years ago

alias tf='tail -f'

I saved you three more!

le_lenny_face• 11 years ago

GRUB_CMDLINE_LINUX_DEFAULT="init=/usr/bin/tail"

Maximum savings!

igorgue• 11 years ago

Wait... Isn't less gonna read the whole file at first? That might suck for files that are already huge.

quicklyfrozen• 11 years ago

No. I use less to navigate gigabyte log files quite often (it's more efficient then vim).

64bitbrain• 11 years ago

I use "tail -f" most of the time. Sometimes, I just dig more and use grep with it.

tail -f sys.log | grep NETDEV

But I would definitely give this a try, thanks for sharing.

zobzu• 11 years ago

U dont tell me what to do! i like my tail

/thefox

nailer• 11 years ago

On current Linux distros, you're more likely to use:

    journalctl -u service-name -f

-f, --follow Show only the most recent journal entries, and continuously print new entries as they are appended to the journal.

barnacs• 11 years ago

I prefer the more expressive

  journalctl -fu service-name

tstack• 11 years ago

There's also lnav (http://lnav.org), the Logfile Navigator. It can do what 'tail -f' and 'less' do plus: syntax coloring, filtering, loading compressed files, interleaves log messages from multiple files, and more.

Many of the comments I see on here about using '-F' with tail instead of '-f', live searching, and so on are handled in lnav by default. I would really encourage folks to give it a try.

kolme• 11 years ago

I use tail -f inside tmux anyways, so I already have the extra feature less offers ("navigation mode", searching, etc) without giving up the "watch multiple files" feature.

A much nicer alternative, IMHO.

thebouv• 11 years ago

Searching with less is a cool feature, but I think the best thing I learned was to use -F instead of -f with tail thanks to the comments on the article and HN.

Of course I'll probably fail to use any of it because of finger memory just typing out tail -f for me.

realrocker• 11 years ago

$make -j16 showcommands > build.log 2>&1 | less +F

ctrl+c...

ctrl+c * 1e9 impatiently

...

build stopped

oops

ephexeve• 11 years ago

Nice!

sixothree2• 11 years ago

Linux just really needs PowerShell.

zer0rest• 11 years ago

hahahaha, No.

sixothree2• 11 years ago

Enjoy your parsing text files. I'll work with objects instead.

jetpks2• 11 years ago

If you're using a modern terminal with scrollback, you already have the ability to pause, and scroll back.

    # tail -f busy.log
    < see something of interest >
    ctrl+s # Stops flow of output.
    pgup/pgdn for navigation # fn+up/dn for OS X users
    ctrl+q # Continues flow.

No need to reinvent the wheel, the functionality you want is probably built into the tools you're already using.

prakashk• 11 years ago

This is not a replacement for searching for a specific string in `less` which highlights the matches, and eliminates the need for scanning the text manually which is harder and prone to missing information.

falcolas• 11 years ago

Most terminals also offer searching capability, which do not result in disk seeks on the remote host.

jetpks2• 11 years ago

Correct, however the author is saying that there's no reason to ever use tail unless you're tailing multiple files, which is false. Most of the functionality you want is already built into your terminal emulator. If you want slower updates (`less` uses 1 second polling, vs `tail` [inotify]), and the ability to search, by all means, use `less`.

Yizahi• 11 years ago

But it won't show me old parts of the log and I usually want this.

sciurus• 11 years ago

If you're looking at log files, a tool I've started to play with is http://lnav.org/

= In Your Terminal = Many logging tools, like Splunk, provide great features but are optimized for large-scale deployments. They require installing and configuring servers before they can be effectively used. There is still a need for a robust log file analyzer for the terminal.

= Easy to Use = Just point lnav to a directory and it will take care of the rest. File formats are automatically detected and compressed files are unpacked on the fly.

= Improved Presentation = Log files are a wealth of information, lnav can help highlight the parts that are important and filter out the noise.

beernutz• 11 years ago

That looks very nice! Thanks for the info. 8)

crypt1d• 11 years ago

While I understand that the author is just trying to be helpful, the provocative title of the article makes me want to scream: "Stop telling me which tool is right for MY job."

tristor• 11 years ago

I use tail -f mainly for tracking something end-to-end through multiple log files because it's pipeable to grep or awk, where less is not. less +F is cool too, but tail -f is more useful when doing complex log analysis on the fly because it follows standard UNIX I/O behavior.

ircuse• 11 years ago

Put that kind of suggestion in coderwall.com

pearjuice• 11 years ago

Stop using [commonly accepted, proven method] and use [obscure alternative]

Textbook HN hit.

reidrac• 11 years ago

Not convinced, still like tail -f because you can hit enter a couple of times and there you are... a nice visual mark to wait for new data without getting confused by existing content.

All this in my humble opinion. less is useful and I may use F to wait for data if I was looking for something in old logs, but for new data I still like tail -f :)

prydonius• 11 years ago

I was interested in the significance of the plus for this flag. If anyone else was curious: from the manual, the + flag is for initial commands to less, so this is equivalent to running less and typing F.

agopaul2• 11 years ago

For semi-large file (1/2GB+) less takes seconds if not minutes to count the number of lines (it read the whole file) so you can navigate and search across the file. In that cases tail -f and grep are still way faster than less, though less is a handier tool

toddkaufmann2• 11 years ago

You don't have to wait. You can turn that off with '-n'.

When you jump to the end of the file ('>' command) you'll see "Calculating line numbers... (interrupt to abort)" and interrupt (ctrl-C) here will also turn them off.

agopaul2• 11 years ago

I didn't know about the -n switch. Usually I need to get to the bottom of the file and find the last occurrence of a string in the logs (G, CTRL+C to stop counting lines, ?string to search) and the slower part is waiting for less to match a string going backwards on the file. Will check if the -n switch solves the problem

laumars4• 11 years ago

We all have been there: You are watching a file with tail -f, and then you need to search for something in this file, or just navigate up and down. Now you need to exit tail (or open a new shell), and ack this file or open it with vim to find what you are looking for. After that, you run tail again to continue watching the file. There's no need to do that when you are using less.

There's also no need to do that if you're running tmux, screen or have navigation tools baked into your terminal emulator.

Not that I'm trying to dismiss the effectiveness for +F for those inclined, but as the author acknowledged, +F also comes with some usability issues that -f does not (namely working with multiple files, and piping output into grep et al). Plus learning to navigate though terminal history is a useful skill to have in other situations anyway, and utilities like tmux are actually a very handy tool to use for a whole plethora of additional reasons too.

So kudos to the author for his recommendation and providing helpful write ups to future sysadmins, but I'm inclined disagree with him and instead recommend people stick with -f and learn tmux instead.

TallGuyShort3• 11 years ago

Not if you also need to search things that weren't at the end of the file when you started tailing - which is very common with log files.

laumars4• 11 years ago

Generally you wouldn't want auto updating like the less +F or tail -f if the content you wanted was at the start of the file. However you can still work around those rare instances by specifying the -n flag. eg

    tail -n 2000 -f

The beauty of this is a file with less that 2000 files will be read in it's entirety, and you're gracefully managing larger files by cropping out the surplus data at the beginning.

And the best thing about this method is you can still pipe grep (which you couldn't do with less) so if you are writing out ~2000 lines rapidly enough that the content you want wouldn't be at the bottom, you can manage the text stream more efficiently (ie grep -v out stuff you don't want or only grep in the content you do want)

I should add that I am a fan of less on many occasions, but in this instance the piping ability of tail is a deal breaker when working with larger files.

kakakiki• 11 years ago

I see that tmux doesn't come as part of standard ubuntu installation. So I think that puts it at a disadvantage for not being omnipresent.

laumars4• 11 years ago

Neither is about 99% of the other software that Ubuntu desktops and servers run daily. Hence why we have software repositories and user friendly package managers to make installing new software a breeze:

    apt-get install tmux

w4tson• 11 years ago

+1 for Commandline Fu. I love it when you see a colleague at a terminal and you say "Whoah, go back, what was that you just did?". It's kinda beautiful really, the way everyone has slightly different methods for common dev tasks at the commandline.

My method is usually '+G' to go to the end of the log file and check the damage report. Quick reverse search with '?' + search term to find last error, then probably hit 'n' to find the next previous any other occurrences to determine how frequent it's popping up. If it looks like it's a recurring problem i'll '+F' to see follow latest output. Then CTRL+c to quit that mode.

tail -f still has it's uses for cases as pimlottc mentioned. I like to put a bit of distance between the last bit of output. Especially if its a particularly repetitive and lengthy stacktrace.

relaxitup• 11 years ago

I use tac file |less often to start at the end of the file..

amelius• 11 years ago

Why not just pipe the output of tail -f through less?

bmoresbest55• 11 years ago

This is pretty awesome. I have always thought that "tail -f" was a little limited but still useful. Any how, great post!

jordanpg• 11 years ago

For something simple and very lightweight for Windows development, check out BareTail: http://www.baremetalsoft.com/baretail/

BorisMelnik• 11 years ago

"here you have pretty much the same behavior"

what is meant by 'pretty much?'

UserRights• 11 years ago

What do people (you) think about browser based log viewers like e.g. logio.org? I like to comfortably have all the logs in the browser but do not want to go full ELK (or anything in this category) stack just for a few servers. But I am not sure if there is some better solution? Multitail is great, but sometimes just opening a new browsertab is even greater...

Animats• 11 years ago

It's amusing to read this just as, for the first time in months, I have a "tail -f" running. I just converted a medium-sized system from Python 2 to Python 3 (this is not fun; I had to fix or work around five bugs in external modules), and deployed it this morning. So I have a "tail -f" running in "putty", watching an Apache server error log. (I know, retro.) This is just in case there's some new Python-level error; operational errors are logged to the database. The log is quiet, and soon I can stop watching.

xxdesmus• 11 years ago

Imma just gonna leave this here: http://seclists.org/fulldisclosure/2014/Nov/74

soyuka2• 11 years ago

With `tmux` there is a visual mode that allows to `tail -F` with search, selection etc.

ewindisch• 11 years ago

I would be careful about such casual use of less: http://seclists.org/fulldisclosure/2014/Nov/74

shirro• 11 years ago

Perhaps neovim with terminal mode and tail -F might be the best of all worlds.

ahomescu1• 11 years ago

I think I'll do the following (as a joke, surprised no one did it already):

  $ alias stalk='less +F'

r0naa• 11 years ago

Interesting.

I always preferred

  watch -n 1 -d 'tail /path/to/log/file'

to tail -f

because of its nice highlighting feature.

pimlottc3• 11 years ago

watch is one of the great unsung heroes of unix tools. Discovering it was one of those "I wish I knew about this years ago" moments. Unfortunately it doesn't seem to have spread much beyond GNU/Linux platforms.

jimmaswell• 11 years ago

I've literally never had this problem and nothing is wrong with tail -f for me. Quitting tail to use grep on the file is anything but inconvenient for me.

monokrome• 11 years ago

I think that it's worth noting that you should still use `-f` if you are viewing a file over SSH that is being appended to a ton and you don't need every line. SSH will require that every line makes it to your terminal over it's secure connection, so you will be bottlenecked and most likely won't be viewing the latest messages. Everything will be queued.

decentrality4• 11 years ago

Doesn't read ANSI color codes! Looking through manual for that.

decentrality4• 11 years ago

SOLVED: less +F -R <file>

Interprets color codes as RAW, relaying them to the screen as-is.

awalGarg• 11 years ago

Haha I didn't know a lot of people didn't know about this. I am one of those people who likes to read man pages :D Another favorite one of mine is the `v` switch to quickly jump to the editor from `less`. Pretty handy!

sbov• 11 years ago

For log files that move particularly fast, I prefer to use "watch tail -n 100" so I don't choke my connection.

sigzero• 11 years ago

Solaris 10 doesn't have the -F flag.

luckymedonwon2• 11 years ago

Can you hack face book account

luckymedonwon2• 11 years ago

Can I hack someone's pay face book

decentrality4• 11 years ago

It would be awesome to remove the "Waiting for data... (interrupt to abort)" message.

decentrality4• 11 years ago

Passing -Pw without a prompt at least gets that down to "... (interrupt to abort)"

fidz• 11 years ago

Thanks! This is really great trick. I will obviously use less +F for tailing single file.

Meanwhile, tail -f still useful for simple tailing to multiple machine, like

    function dogfight_tail {
     logfile=/var/log/nginx/access.log
     pids=""
     for box in 02 03; do
       ssh lb$box tail -f $logfile | grep " 500 " & # find error machines
       pids="$pids $!"
     done
     trap 'kill -9 $pids' SIGINT
     trap  wait
    }

    dogfight_tail

mdekkers• 11 years ago

...or use multi-tail

snambi• 11 years ago

wow... this is really a nice coomand

aweiher• 11 years ago

its not better for me, hitting enter is essential for me when using tail

fsniper• 11 years ago

I just had an SRE screening and one of the questions was

"What is a linux command that's mostly not known?".

I could not remember anything that's special, at least for me at the time but "less -F" poped up to my mind. Thank you :)

Oh now I can think of ccze, column and tac. Interviews..

Stop using tail -f (mostly)

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