A system slows down and tcsh consumes a lot of memory due to a corrupted .history file

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 2.1
  • Red Hat Enterprise Linux 3
  • Red Hat Enterprise Linux 4
  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • RHEL5: tcsh-6.14-14.el5-x86_64
  • RHEL6: tcsh-6.17-8.el6.x86_64

Issue

  • The data in the file ".history" becomes malformed and its file size gets larger and larger.
  • Each command history should be recoded in the file with a timestamp line a command entry line which should end with EOL(End Of  Line).
  • Example of normal .history file: 
$ cat -n .history  
\#+1289787344  
set
  • A timestamp and a run command entry are not recorded by turns. Not a run command entry but a timestamp is recorded unexpectedly (see the line 4). Additionally, some entries are merged unexpectedly (see the line 6 and 7 below).
  • Example of malformed .history file :
$ cat -n .history  
 \#+1289787344  
 test  
 \#+1289787367  
 1289787366  
 \#+1289787367  
 128978\#+12897\#+1289\#+12897test  
 \#+1289\#+12897testls\#\#+1289787401l12\#+1289787402  
 st
  • A system slows down because csh uses a lot of memory to read such a large .history file.

Resolution

  • We have released following 6.2.z erratum: http://rhn.redhat.com/errata/RHBA-2012-0687.html

  • We have released following 5.9 erratum: http://rhn.redhat.com/errata/RHBA-2013-0052.html

    Note: we released errata only for tcsh617 package for RHEL5 system. So if you're using tcsh package 'based on tcsh-6.14), you need to replace tcsh from tcsh package to tcsh617 package.

  • We will not address this issue on Red Hat Enterprise Linux 2.1, 3 and 4.

  • Temporary workaround:

    • Consists of setting the following in ~/.cshrc or on the command line:
    set savehist=
    • The above will prevent any writing to ~/.history file (even the empty file still gets truncated every time) thus there won't be any delay in running scripts and no bug will show up.

Root Cause

  • The main issue which should be fixed is that tcsh does not handle ~/.history file exclusively. The "merge" option causes possibility of a little more unexpected behavior with warning mentioned in man page regarding the "-S" built-in command:
 history \[-hTr\] \[n\]  
 history -S|-L|-M \[filename\] (+)  
 history -c (+)  

 With -S, the second form saves the history list to file-  
 name. If the first word of the savehist shell variable is  
 set to a number, at most that many lines are saved. If the  
 second word of savehist is set to ‘merge’, the history list  
 is merged with the existing history file instead of replac-  
 ing it (if there is one) and sorted by time stamp. (+)  
 \____Merging is intended for an environment like the X Window  
 System with several shells in simultaneous use. Currently  
 it succeeds only when the shells quit nicely one after  
 another.\____
  • Additionally, both a value greater than 0 and "merge" option are set to savehist on csh and this is the default setting in Red Hat Enterprise Linux 5.4 or later:
 $ set | grep savehist  
 savehist (1024 merge)

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